Now the simple answer is theoretically you can, but you shouldn’t.
Knob tailed geckos are found all across Australia, so there is a lot variation in temperature and habitat differences. Tropical species such as N.Asper will want different species to you N.Levis. Another factor is the stress it can put on animals. Knob tailed geckos are territorial and males will fight other males.
Also hybridising is another thing that can happen.
I would strongly do not recommend housing multiple species of the same genus together. For something as small as knob tailed geckos, it would be much cheaper to buy a small fish tank or tub than have a dead knob tailed gecko.