I’m not the smartest tool in the shed, and do not battle in gyms very often but when I see an empty spot, I throw something stupid in there. Like that Kingler I named Dum A Chum?.

Or my Jynx, affectionately names BEWBZ:

Now, me being a noob, I thought only players on the same team AT THE GYM could feed berried to boost thier CP.

Today I found out that THE TRAINER THAT PUT THE MON THERE can feed any of them in the gym from wherever! Just go to you Pokedex, select the one that is at the gym, and click “GO TO GYM”. Or you can do it from your Trainer menu if you scroll down to visited gyms.

Apparently no one else knows this, or they all ran out of berries like I did. RIP this gym, I guess.