I am preparing a backsplash in my kitchen for tile that will be applied between the counter top and the bottom of the cabinets. The existing paint is gloss enamel, probably latex. I think I should prime over this paint but am not sure how to prepare the old paint. I planned to put Kilz2 over the old enamel but how do I prepare the gloss paint, don't want to sand if not necessary. Already cleaned the surface with TSP.

You should do at least some basic sanding for the primer to have some grab. Use 220 grit. What are you going to use for mastic?

I will be using thinset. I actually use TSP to clean it up at the same time I used scotch brite pads so I think I scuffed it up well enough. Thank you for your response.

If you used a scotchbrite you are probably OK. For smaller areas and over existing surfaces, I usually use Acryl Pro, from HD. It has a very good set and stick capability. A bit slower to completely dry but it's easier to use and safer on the skin. I just did a 24 sg.ft backsplash with 6X6 and it came out great, customer very happy. I use Chick Fil A coffee stirrer sticks for spacing. Good luck, Brian