If my Radiant Greninja has already used its "Concealed Cards" Ability during my turn but then goes out of play, if I bring it back into play can I use "Concealed Cards" again on the same turn?
Yes, you can.
Source: TPCi Rules Team (2022-06-16)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH10_46
SWSH10_46