Ticket JR and private line same journey?

Good morning
I will be travelling to Shikoku in March and April, by train without pass.
1St question :For the same train journey, if the journey includes a private line and a JR line , is it possible to buy the full ticket at once at the departure station or do I have to buy the ticket at the station where I change train as JR/private?
For example 1st line JR : buy ticket JR; 2nd line private line : buy another ticket at the railway station so allow enough time stop; 3rd line JR or private line : same , buy another ticket.
Or may be it is possible to buy the train ticket from the company employee in the train without penalty?
Thank you so much for your attention

Gislaine

is it possible to buy the full ticket at once at the departure station or do I have to buy the ticket at the station where I change train as JR/private?

In most cases you have to buy separate tickets. There are some exceptions, e.g. JR trains running on non-JR tracks.

Or may be it is possible to buy the train ticket from the company employee in the train without penalty?

Usually you cannot enter the other company's stations without a ticket.

If the trains accept IC card then you don�ft need to buy separate tickets.
It sounds more complicated than it is. Just follow the flow.

I strongly recommend you to buy All shikoku rail pass 7 day=13500 yen cover unlimited travel in JR and non JR trains,ferry and some local bus in shikoku prefecture

Thank you very much everybody for your quick responses :) :)
I thought, without having checked it in details, that JR pass was valid only for JR lines.
In fact it seems that possibility of using JR pass on private lines depends on the regions/areas.
All is explained here: https://shikoku-railwaytrip.com/railpass.html.

Happy new year to you with ,maybe, travels.
Gislaine

For the same train journey, if the journey includes a private line and a JR line , is it possible to buy the full ticket at once at the departure station or do I have to buy the ticket at the station where I change train as JR/private?
You are describing two different types of trip here.
(A) A journey that incorporates a private line for part of the journey you may have your JR ticket (or pass) and need to pay a supplement on the train for the non-JR portion. There is a regular trip I take that ends at a non JR station and depending on which way I approach this particular spot, I either need to pay for the non-JR portion to exit the station, or am able to get a ticket that covers both the JR and non-JR portions - it is case specific.
(B) A journey where you need to transfer to a different train, i.e. from a JR service to a non-JR service, the usually situation is that you need to use a transfer gate, or exit the JR station and then enter the non-JR station - this occurs in hundreds of cases across Japan. Jr cannot sell you the non-JR ticket - you need to allow time for the transfer and getting the second ticket.

If you list your specific journey, that would be helpful.
The suggestion (above) to just buy a Shikoku pass (which isn't cheap) without knowing your schedule and potentially wasting a ton of money isn't good advice.

You can buy shikoku highway bus pass
unlimited 3 day travel for 8800 yen

By studying the details of my routes and schedules, I only find one private line : Tosa Kuroshio Nakamura.
For the pass, indeed , if the fares (search through Navitime,Jorudan,Ekispert) are true , I don't need pass .
I will be travelling for 3 weeks in Shikoku, so I'll see how it goes .

Thank you every body, may be this conversation will help others travellers.
Gislaine