The abilities of a unit can be seen in its "unit card" when it is selected as small icons, and I can hover over them for information. However, in late game many units (especially ones upgraded from old units) get so many abilities from promotions, buildings and social policies that the icons extend so much left they go under the unit icon and even flow off the screen, preventing me from hovering over them.
Is there are way to see what those abilities are? Perhaps there's a UI mod to change this?
Best Answer
After some mod-browsing, I've found a mod called "All Promotions description tooltip". It adds a tooltip when hovering over a unit's icon in the bottom-left (its symbolic icon, not its painted portrait), which nicely lists all the promotions and their effects.
Before:
When hovering over that orange Frigate icon:
So this solved the problem for me, and I highly recommend this mod.