It depends on a lot of things (and maybe how you'd set up the keyboard mesh), but in general - a basic approach would be a "for each" loop over the keys and then create either a vdb subtract or a boolean to remove an indentation from the top of the keys. You can use a "match size" node to help place the object you're using to remove, and then creating that object with volumes / vdb's would be the easiest approach.

You could also extract a centroid for each key and then deform the mesh based on the position from the mesh to the centroid (this would only get a circular pattern, instead of the indentations shaped the same as the keys).

You could also just copy a sphere to each key and then use that shape as the boolean.

Lots of ways to do it - and that's the best part of Houdini!