The mixolydian pentatonic is just the major pentatonic starting on the 5th scale tone (or the 7th for the minor pentatonic). It's usually called the Dominant pentatonic scale.

A minor pent is A, C, D, E, G, A.

To get the mixolydian (dominant) pentatonic scale start with G (the seventh). You get G, A, C, D, E, G.

It's just like figuring out the modes for the major scale, although instead of using the major scale you just use the pentatonic scale and then go from there.