Sculptors observe and find the forms of the object that they are sculpting and then create forms to mimic what they observe. When drawing, we do the same. We find the shapes and then draw the shapes that we see. ... Think like a sculptor when drawing, and your drawing skills will improve.

Should I learn to draw or sculpt?

Technically, no. You don't need to know how to draw to become a decent sculptor. Learning to improve the principle skills that make someone better at traditional drawing and sculpting automatically improves one's ability to sculpt, model, and design digitally.

Do I need to draw to sculpt?

You don't need to be able to draw, but it helps. And you will find most successful modelers can. While they are different types of tools, ultimately drawing and sculpting are less about the technique and more about taste, design sense and having clear enough concepts that you communicate them regardless of method.