I've been told that New Krypton and all of the Kryptonians living upon it at the time were all killed when General Sam Lane's agent Reactron blew up, taking the planet itself with him and even Supergirl's mother Allura.  I've also heard many of Zod's soldiers were in the process of invading earth in retaliation for something else Lex and Lane had done, no idea if any of them still live or if they were locked up, etc
 
What I'd like to know is how many Kryptonians, if any, survived this act of genocide and if any of them are still living on earth, perhaps in hiding after all that went down.

As many as DC needs.

"As many as DC needs. "

A couple thousand 

Most of the survivers are in the phantom zone...the other probably are hiding on earth or left earth.They will be back to probably kill Superman for betraying them.

i'm sure more will pop up eventually
they'll say something like 200 but give us 500

Superman doesn't know. It was something like "if they're out there, they don't want to be found."
DC writers will pull some out when they feel like it.

let us see im thinking a million of them but if an invasion was going to happen well we all need to process more Kryptonite or find Batmans secret Kryptonite cave

I don't know there is a family on earth like kryrpto and more and that one city was taken by braniack so i would say a few thousand