stain bleeding through
 

I primed a wall with Kilz-2. This over a previously painted wall (drywall) that had something spilled on it.
When the kilz dried, I noticed that the stain bled through.
I heard of using some type of varnish sealer but, can't remeber exactly what I should use.
Any suggestions?

A very light coat of paint from a spray can does wonders for hiding stains.

If you had used Zinzeer 123 this would not happen I find using Kilzs is like priming with milk. A good stain killing primer has shellac in it.
A spray paint not made for priming wood or sheetrock may contain fish oil which paint will not stick to. (like Rustolium) And may leave a shinny spot when painted.
I'd just give it another coat of primer and paint it.

so he/she doesn't have to strip the old paint///old primer before adding a new layer of primer?

Nope, painted the wall to see the outcome and the stain didn't bleed through.
Applying primer is different than applying paint.
You just need a thin even coat of primer to hold the previous paint from coming through and the new paint from going in.