"Remember it" is very close to the meaning. The common saying is "let it soak in" or "soak it in" and it brings up the imagery of a sponge soaking up some liquid. I hear or use the saying most often after a sarcastic comment where it may take the person a few seconds to realize the joke or lesson I just told them.

I've never heard someone say just "soak it" in that context. Usually they're talking about soaking something in a liquid. But there is also the expression "let it soak in". Which basically means wait a few minutes so that you'll remember it or so that it will register in their minds.

I've not for once heard that phrase either but considering the situation of the actions, it might also means "get something into your head" more like "Remember it".

Could it have been "suck it"?