how to create an additional volume on a spherical surface?

There are a few ways to do it, I'd do it this way to start:
- Start with sphere
- On a regular reference plane, create sketch geometry to define the location of the new plane
- Create a new reference plane
- Sketch desired shape(s) on this new plane
- Extrude or perform other functions as required.

There are many ways to do it, I made a part To Show you the method I use, I leave the file part of the sphere and some pictures so you can analyze and clarify additional questions, I hope it is useful, good luck