korea-japan rail pass, in japan

we have bought the korea-japan rail pass,which is inlcluded the travel pass from seoul-busan-fukouka-osaka, in hongik travel agent in seoul korea. All the pass between seoul-busan, busan-fukouka, are already set.but they said they can not make anything with the fukouka-osaka from seoul, as it is an open ticket by japan rail. my questions are :

1.can we use this ticket for all kind of Japan Trains?

2. if not, what kind of train that we can use?

3. is it any certain or kind of the night train that we can use for this ticket, to travel from fukouka by night and arriving osaka in the morning? what the namae of the train? we would like to travel to osaka from fukouka on 25 december or 26 december

4. should we make the reservation of the seat with this ticket to travel from fukouka-osaka?

5.if we should make the reservation, where should we make it?

6. if the reservation should be made only in Japan, can we make the seat reservation from the website/email?

7. what happened if all the seat are fulled, what should we do with the ticket? will jr refund it?

thank you

can we use this ticket for all kind of Japan Trains?

I am not familiar with the pass. Do you have some link to a page that introduces the pass or at least the official name in Japanese or English?

In any case, it is highly unlikely that the pass will cover all trains in Japan. In the best case, it might cover all JR (Japan Railway) trains in Japan. More about JR and trains in Japan:
http://www.japan-guide.com/e/e2019.html

if not, what kind of train that we can use?

No idea. But note that the easiest way to travel between the two cities is by JR Sanyo Shinkansen high speed train. More details are found on the page below:
http://www.japan-guide.com/e/e4802.html?aFROM=2157_2161

should we make the reservation of the seat with this ticket to travel from fukouka-osaka?

The shinkansen trains have unreserved seats which can be used without seat reservations, however, it is always nice to have a seat reservation, especially if you are traveling in a group.

if we should make the reservation, where should we make it?

I don't think it is possible to make seat reservations from outside of Japan.

what happened if all the seat are fulled, what should we do with the ticket?

Then, you should be able to use the unreserved seats. If these are also all taken, I am afraid you have to stand.

But traffic should not be that bad on December 25. Only from the afternoon of December 26 and on December 27, the trains will be very busy due to the starting New Year holidays.