>>40406339I'm the person from Twitter who helped bring light to this, it works identically to SM/USUM.
Exp. Points are scaled depending on the Level of the opponent after KO/capture (like in Gen 5/7). Afterwards, Exp. Share gives 100% Exp. Points to participants and 50% to non-participants.
After running the formula seen on Bulbapedia in a quick calculation, the Exp. given to the Pokémon shown in the picture matched up perfectly.
tl;dr works the same as SM/USUM