sentence translation

Hello, today I was reading a manga in Japanese and I came across this sentence

"しかし　おぬしは　わしに　似んとゴックなったの"

I'm trying to understand the meaning but I really don't know where to turn T__T

Thank you :)

That ゴック bit, particularly in katakana, doesn't quite fit into the sentence. Or can it be that the characters are drinking something together, and the "gulp" sound got sandwiched into the sentence?

The rest of the sentence is like:
- But you turned out quite unlike me.
(Can it be the dad making a comment about the son, saying he doesn't look like himself?)

No.
AK mentioned different word
that is onomatopoeia/擬声語（gisei-go) drinking sound "ごくごく/ゴクゴク(goku-goku)".
https://youtu.be/TxDNsYyaEfI

But this "ゴック" is mis-read/copied "ごつく" or "ごっつく" is correct.
http://thesaurus.weblio.jp/content/%E3%81%94%E3%81%A4%E3%81%84
This word is "mimetic word/擬態語(gitai-go)" "ごつごつ/ゴツゴツ(gotsu-gotsu)" based
means more harder/rough faced than ザラザラ of rocks/stones or something hard item.
https://www.google.co.jp/search?q=%E3%81%94%E3%81%A4%E3%81%94%E3%81%A4...#
But often using for "face" or "body(as muscle)",too as looks/style not only for human/animals
and also strong character as mind(grow up/be adult).
ごっつい顔(かお)：
https://www.google.co.jp/search?q=%E3%81%94%E3%81%A3%E3%81%A4%E3%81%84...
ごっつい体(からだ)：
https://www.google.co.jp/search?q=%E3%81%94%E3%81%A3%E3%81%A4%E3%81%84...
So in this case son or pupil/disciple looks/character dosen't like father/granPa or master/teacher/boss/leader
but no exact about just different face/body or character changed for good/stronger.
Stanfdard setence is
"しかし、あなた(or君/きみ)は私（わたし）に似（に)ないで、(随分と/ずいぶんと)たくましくなりましたね。"

List of onomatopoeia/mimetic words :
http://daijirin.dual-d.net/extra/giseigo_gitaigo.html#id_5-1
Jump to 物の様態・性質
1 固さ・重さ
also jump to 擬声語・擬態語の語形
一回(one time)語形(type)
1「Aい(A+い)」型 in this case (ごつ＋い＝ごつい)
"A" is short of onomatopoeia/mimetic word one sound.

Add(or instead) small つ(= "っ") cases a lot
for meaning stronger as adjective(形容詞/keiyou-shi).
ex)
あつい(hot) is あっつい(really/pretty/very hot from sandard とても/すごく＋あつい)
あたたかい/あったかい
あまい/あっまい
おおきい/おっきい
かるい/かっるい
きたない/きったない but きれい won't be "きっれい"
ちかい/ちっかい
すごい/すっごい

"ゴツゴツ" also sometimes using "beating (low tone) sound" as onomatopoeia
than high tone light weight sound "コンコン/カンカン/コトコト".
But in this case "ゴトゴト/ガタガタ" is best.

And this is no related original Q but
"ごっつい(or ごっつ)" in Kansai region("Osaka" mainly) means
"very/pretty/quite/really/super" when "suprised" instead usual.
Similar word "めっちゃ/めっさ",too.
(short of 滅茶苦茶/mecha-kucha also めちゃめちゃ/mecha-mecha)
https://www.youtube.com/watch?v=NKBtl0oR-1Q
skip to last phrase 3:00
In Manga/Anime a lot of Kansai region(Osaka,Kyoto dialect) words/phrases
also old period words/phrases still mixed a lot.
(Japan is over 2500ys country not so easy to understand)
In present still studying about 古典/古文/漢文 at junior high and high school both.
https://www.google.co.jp/search?q=%E5%8F%A4%E6%96%87%E3%80%80%E5%95%8F...

No worry most Japanese also didn't understand all and perfectly :)

Gokku is exactly no exist as Japanese word listed into dictionary or not
but "Gogg/ゴッグ" was born and living in "GUNDAM" world :)
http://gundam.wikia.com/wiki/MSM-03_Gogg
(It's joke no need remember)

Now I see what could have happened. The word may be ゴツク, with large ツ instead of a small ッ. If it is ゴツク, then the guy who is speaking is saying:
- But you have come to have a sturdy build, unless myself.

"Gotsui" is an adjective meaning strong, sturdy (build of body), rugged, etc.

The way he uses the word おぬし to refer to the on who he is speaking to, and わし to refer to himself suggests the speaker is the older one.

Still if I write out the sentence in a more "textbook" style, taking out the colloquial expressions, it would be:
しかし　おまえは　わたしに　似ないで、ごつくなった　なぁ

Yes, sorry the word is ゴツク with the big "ツ" .

This is the page of the manga.

https://postimg.org/image/8rytrhm6v/

So maybe you could understand better.

I don't understand what わしに似んとゴックなった actually really means.

Now I know that ゴツク means strong, sturdy (build of body), rugged but I still don't get it. It makes no sense to me and I have read the chapter of the manga so I should be able to understand.

I feel so stupid!

Yes, this is definitely ゴツくなった. Oh, so is the one who is saying it is like a "senior" (warrior or whatever)?

I guess he/she is just saying "anyways, you've turned into such a rugged guy, so different from myself," maybe halfway lamenting that he/she is not that mannish or strong-looking :)

Yes, he is a demon! xD

But I'm not sure why he is saying that to him! xD

That looks like old(1970s) framous manga/TV-anime "Devil man" parody.
Left is Devil man(Fudou Akira), Right is Silen(horns shorten???)
https://it.wikipedia.org/wiki/Devilman
https://it.wikipedia.org/wiki/Akira_Fudo
https://it.wikipedia.org/wiki/Silen
http://www.internationalhero.co.uk/d/devilmanvsshirenu.jpg

But they are wearing kimono/着物(wafuku/和服,wasou/和装).
Especially Silen??? costume is 弁慶/Benkei also 山伏/yama-bushi style.
http://www.eonet.ne.jp/~jawa/kabuki/gallery/kanjincyo.jpg
https://en.wikipedia.org/wiki/Benkei
https://www.google.co.jp/search?q=%E5%B1%B1%E4%BC%8F&hl=ja&biw=885&bih...

However, original Devil man is NOT such story.
So guess manga artist's small joke include respect
Devil man is one of famous ごっつい(濃い)顔/face and muscle body character.
Also real Silen is a devil woman so not "he"
and Devil man(Akira)'s mam/elder sister or master/teacher.

What is the title that comic?
Silen??? also looks like another title's something of 鬼/oni(short horns usual) character.
https://en.wikipedia.org/wiki/Oni
That manga's character?

Now I know that ゴツク means strong, sturdy (build of body), rugged but I still don't get it.

Well, depending on contexts, ごつい refers to a person's movement, carriage or behavior, meaning it is awkward, unsophisticated or so.

Separately concerning the sentence in question, it seems more natural to think this ごつい as description of a person's physical appearance, as is explained by beaggai and AK.

One reason is that わし, ごつい and のー/のう are informal and comparatively spoken words.
For example, ごつい is not a word, I suppose, for a master or instructor of Sado(h) (= the art of the tea ceremony, also called "Chado(h)") or Nihon Buyo(h) (= classic Japanese dancing) to use during his/her lessons when he/she describes his/her student's manners.

おぬし is a little archaic word, which may sound humorous now in the modern Japanese.
And, おぬし is used mostly toward the speaker's fellows or those in a lower position; so, in the manga scene, おぬし in the woman's words can let us assume that the man who is spoken to may be her son, student or so.