How mod K2SO?

In a droid team, HK and JE are core. B2 is mandatory for the current meta (ST, SF, Chaze, etc). So K2 has to replace either 88 or 86 (the two common remaining slots, though some would be making the choice between 88 and 100). Since those are both damage dealers, I would say go for damage. With solid counter chance he'll be activating frequently (like B2), so every bit of extra damage helps. I could also see tenacity emphasized to maintain that counter chance.

I have little to no experience with rebel teams so I'm unqualified to answer to that end.