Question

______ mas despacio, por favor. No entiendo.

Answer 1

This translates to ______ slow down please I don't understand. If you asking one person your answer would be puedes.

Answer 2

This translates into:

"______________ more slowly, please. I don't understand."

Since the second sentence is "I don't understand.", it seems to me that you need to ask the person to speak more slowly.

If it is a person you call tu, then write "Habla"
If it is a person you call usted, then write "Hable"