Okay, I’m not a professional but pretty damn close. Here’s my take:
First, that print looks like SILK PLA. If it is, stop where you are and print it again in PLA+ or PETG.
SILK is extremely hydrophilic, meaning it absorbs water.
Second, always start off by sanding your raw print. I usually go with a 80g, clean the piece and start with filler primer. If you layer lines are particularly bad I’ll use spot putty, sand that as smooth as I can get it then start applying filler primer.
Last, if you have access to a HVLP sprayer, catalyzed primers like Evercoat Featherfill G2 are unbeatable when post processing prints.