I have only worked with a small amount of granite slab.
I have however "bullnosed" more granite tiles than I care to admit and the process is the same.
The BEST way is to take your slabs to a fabricator and let them run them through their edge polishing machine.
This will produce a perfect bullnose with no wavy appearance due to human error or the varying hardness of the stone that will allow the sanding discs to cut in at differant rates.
If you are brave and want to do it yourself:
You need a varible speed angle grinder( 1000-3500 rpm )
diamond cup wheel ( 36 grit )
Set of wet sanding discs: 50, 100. 200, 400, 800, 1500, 2000, 3000 and final buff.
rough shape the edge with the cup wheel, dry.
Use all the discs wet until nice and shiny.
Very labor intensive. I never do it anymore except for special pieces, repairs or inside profiles for undermounted sinks.
Have it fabbed.
KT
Oh, did I mention the discs are about $40 each and the cup wheel is $120ish and the grinder is about $300.