There are a couple of ways you can tackle it in Fusion 360. You can use the Emboss function or the Thin Extrude function on Fusion 360 to create raised lines in a pattern on the surface of your handle.

I would estimate that a depth of 1 mm, maybe 2 mm at most, is a good trade-off between fidelity in printing but without trapping too much dirt.

Yes, you do need to be careful with these finer details on nylon SLS – remember that there will be some shrinkage of the printed nylon (generally 0.4%), and also some fine details may be lost in post-processing. I agree with Eddie that around the 1 mm depth is probably a good starting point.

Since you’re using Fusion 360, you can use the material library to simulate the nylon powder you’re using (I’m guessing Nylon 12?) to get a better idea of the dimensional details that would work well. You also don’t necessarily need to get it perfect on the first run – try a few different options or patterns (like embossing vs knurling) to see which you like best.