Unlike Necrotic Ooze in a previous ask, Experiment Kraj can actually benefit from the weirdness of Leveler creatures and gain the activated abilities granted by their levels. This is because Kraj looks at the abilities that a creature currently has, not what its printed abilities are.

So, if you have an Enclave Cryptologist with two level counters and a +1/+1 counter on it, Experiment Kraj will gain “Level up 1U” and “T: Draw a card, then discard a card.” from it. When that Enclave Cryptologist levels up to level 3, Kraj will lose the looting ability and gain “T: Draw a card.” since Enclave Cryptologist lost and gained the same abilities.

And no, putting level counters on Kraj won’t give it access to higher level abilities of any leveler creatures you control.