How can a dishwasher move up to a prep/line cook?

You're right but it can't hurt to be told the extreme. If you're the kind of person that naturally veers to the stupid bum who never shows up your normal might not be good enough.

for perspective i completely avoided the dishwasher position and went right into garde manger with no experience and only quit because the chef owner was an asshole

Give the kitchen manager or head chef some weed and oxys, and tell him or her you want to learn prep. They're all degenerate druggies.

Btw guys, I'm not trying to make this a career. I like cooking,but I'm also gonna go back to school for engineering. Just trying to move up to cook just for experience and skills becuase I love to cook. I know cooks make shit pay. Waiters usually make a cooksweek pay in one or two nights in tips kek. Only worth it becoming a executive chef or a owner for a successful restaurant

When you have extra time ask if they need any help with prep. Do a few simple tasks to learn. Eventually they will trust you to do more. Learn more. Pick up a shift when the salad guy calls off. Onto fry or grill. Etc.

I actually don't know because in both jobs I've done I've just been trusted right away with both jobs, one is even a japanese restauraunt

Find a pet rat

This. Even if you just get some of the skills and aren't actually certified, so long as you can find shady landlords you can still get around $70 an hour for most trade work.