Question

Give me your guitar. Change into
interrogative negative

Answer 1

.........

'Will you not give me your guitar?'

I guess this should be the answer!

............

Answer 2

Will you give me your guitar? – This is an interrogative sentence. But if you want to change it into interrogative negative then you can use it as “will you not give me your guitar?” when speakers is expecting a certain answer for his or her question, then it can treated as interrogative negative sentence.