Normally you can see that via the checksum, that'S how it works in EU4 and CK2. When you start the game, the launcher says v1.xx in the corner, followed by 4 characters in brackets, this is the checksum. Once you started the game, versionnumber and checksum will be displayed in the main menu as well. If the checksum is the same, achievements should work, if it's not, they don't.
However, as of 1.02 no mods seem to work with achievements, even something as simple as adding a few more flags disabled achievements for me, despite the checksum not changing and no other indication that achievements are obtainable (you can play ironman without obtainable achievements, so that's no indication).
So, if you want to play for achievements, at the moment I would recommend playing without any mods.