What levels does linoon pick up different stuff and what level.?

It can pick up different item depending on it's level and where you are.

The higher the level,the better chance of getting a better item.

The ability Pickup allows your Pokemon to pickup a item after a battle. It's really hard to determine, so you just need to keep getting into random battles and hope for the best.

It doesn't it just picks up random stuff.

Yeah, they get better stuff at higher levels, but not always. It changes about every 10 levels-if you really want the whole stats on what they get frequently, infrequently, rarely, etc, check out the guide from Nintendo-there's a chart in the beginning section. Sometimes it's fun to wander around with a Meowth, a Zigzagoon/Linoone, a Phanpy, an Aipom, etc., at all different levels, all in your party at one time. Just run around getting into random battles and you'll get tons of stuff, just keep checking to see if they got something. Sometimes it's easier if the pickup Pokemon is first in the party, but not necessary at all. I almost never buy anything at all because I pickup so much stuff! You can always sell what you don't want!

There is a chart on this site:

http://www.serebii.net/games/ability.shtml#pickup

Levels doesn't mean a thing, it's his ability that lets him pick up random items.