depends on each group.
for example the group I'm in has a different meaning for Quality Checker than the one I managed 10 years ago. The group I managed 10 years ago, QC was to only check for grammar.
The
Quality Checker in the current group I help is a sort of jack-of-all-trades. They are able to fix dialogue grammar and sentence and tone, align dialogues to make it look nicer (Translators already typeset the chapters), put in proper SFX if needed (it helps I do Chinese webtoons, less fancy sfx), and fix minor cleaning issues. Basically what it says on the tin. To check for quality.
there's also
Compiler, you grab the raws from websites (they're usually in short pieces separated at weird as positions) and stitch them together into long page so the cleaner/redrawers and translators would be able to edit chapters easily. Nowadays, it's semi-automated so I am no longer needed to help grab things.
I'm....an old hat. so my position now is everything except Translating
previously everything I learnt was from a website that had everything you needed to know about cleaning and typesetting called
senbonzakura kageyoshi. You can only find it via waybackmachine still. There are other tutorials but this one was my fave.