Pa que sepan = Para que (ellos) sepan. Pa que no sepan = para que (ellos) no sepan. Pa en lugar de Para es un muy, my coloquial, mejor utilizar para.

Depends... Pa que sepan= So they know or So you know (plural) Pa que no sepan = So they won't know

Gracias a todos!

Yes the literal translation it's: so you/they know. But coming from a dominican guy he is using it more like slang, something you say after you do something cool or say something deep.

Pa = (para) Para que (ellos o ellas) no sepan (verbo saber).