My sister lives in Las Vegas, NV and her daughter’s father lives in California.
She wants to apply for child support but doesn’t know where to start this at. Would she need to apply in Nevada or California?
What child support laws apply in her case? (Nevada or California child support laws/where the child resides or where the father resides?)

If there was no previous court action jurisdiction is where the child lives.

Did she just move to Nevada ?

As far as I know (without examining in detail the pertinent statutes of both states), she can sue for child support in either state. The law of the state where she sues applies.

It's called "forum shopping".

Did she just move to Nevada ?

No. she's been there for several years now.

SHe starts in Nevada where her and the child lives. The only reason why I had asked about her living there was to find out residency. If the breakup had been recent and she just moved there then California would have been the place to file.

So she is safe to file in Nevada.