Q: Given a travel related situation, and given a specific question about the situation, summarize the question into a title
I have made Sihanoukville, Cambodia, my travel-around-Asia operations-base for some time now. Now I need to travel to Europe and back... To save some cash on tickets, I will be going to the Thai border by bus, get a visa and fly with Finnair, then return back to Bangkok, catching a bus back to Sihanoukville.

It suddenly hit me that when returning I will be landing in Bangkok and it's my final destination. And I might be asked by Finnair when boarding for proof of onward travel even if I started my journey with them in Thailand. And usually bus tickets do not 'cut it'.

I have Lithuanian passport.

Do I need to get proof of onward travel for my return flight to Thailand, even though I am using the same company (Finnair) to do the round trip to my original destination?

A:
Going from Cambodia to Europe via Thailand and back. Do I need proof of onward travel for the return flight?