Thai partner will go to Europe soon, needs to apply for Schengen Visa. No problem.

Question=

What do you do if the actual travel date is still not certain but you want to avoid cancelation fees, or whatever headache.

To get a Schengen visa without confirmed return ticket?

First of all you need to apply for this visa at the Embassy of the country of first arrival in the Schengen area.

This Embassy will be able to reply to this question.