Slitherine

when awarded Commanders during the game, can you tell their specialty?

Not sure what you mean by specialty.

Aside from the pure gfx the bg of the portrait kinda soft-hints the branch (air -light grey, land, brownish, naval, slight blue-green touch), but that's a bit vague.

If you get awarded a cmdr via objective the ? in the objective window often tells if he's an air ace or else, but not always. However, most importantly the actual stats of the guy can be viewed in the GUI.

As long cmdrs are unassigned (hovering on the right side of the screen), just click them to see the stats in the lower screen GUI.

When they are assigned, select the unit, and click the little info button to see them.

When you click an unassigned cmdr it only offers you units of the correct branch to assign him too by highlighting their hexes.

I meant traits like + attack. or superior defense entrenchment, extra damage by an artillery unit, etc.