It will depend on material thickness, height, and whether you are doing a high flat vs. full flat grind. That said you will probably be in the 4-5 degree range. At least that's where my 3/16" thick high flat ground knives fall. Like this one.
I think I made my first of many errors and ordered a grinding jig that is too steep. The "pre-made" jigs offered were set at 25 deg angles, which seemed to lie-up with some of the things I was reading, but I'm now not sure if that is 25 total from one side to the other. The jig looks ridiculously steep, so I'm not sure I can even use it...
My suggestion is to try a flat grind, with a convex edge. You can increase or decrease the degree of convex to fit the application of the blade, and in the process eliminate the "shoulders" on an edge that is sharpened at angles, which adds to the cutting resistance of a blade because of the "wedge" that's created when sharpening a blade with any type of fixed angle(s). The overall idea being to have minimal or no angled bevels on an edge..... the difference in cutting performance versus edges that are sharpened at angles is very noticeable, and in most cases very dramatic.
Hey Top, I second Eds suggestion. I learned the slow way of what position works best for me and my grinder. As far as degrees that doesn't come into play till sharpening for me.
I just ground a half a flat on a blade and learned how my hands an body worked at each point of the motion. I still have issues with over or under grinding my blade tips. Here is 3/4 of my full flat pre ht with 3 or 4 errors in it to fix still.
When you grind your flat you want one smooth surface. (If you already didn't know)