Correct answer:
Blank 1: No respires
Blank 2: Tú no respires
Commands in Spanish are part of the mood called the imperative that we use to tell someone to do something in a direct way. In this way, respirar is a verb that means to breathe and since we want to tell someone not to breathe using the tú command this is:
No respires
or
Tú no respires
In Spanish, it is common not to include the subject pronoun when giving a command, hence it is more common the expression no respires