What fasteners to sister LVL to 2x6 joist?
Use the Simpson SDW22300 screw installed 6" on center alternating 1.5" from either edge, and starting 3.5" from the end. 

This detail is for a built-up column, but it's the same idea. 

SDW screw pattern

Doing it this way is overkill. It's probably possible to do something similar with 10d nails, but that's more than I know how to do.