What is the bank or brokerage for cash app?

What kind of tax form are you entering?   For what kind of income?  

I dont know much about this, but is for investment for my 1099-B

If you got a 1099-B the payer's name is on the 1099-B. That's the name you enter for the bank or brokerage. If you did not get a 1099-B enter Cash App as the name of the bank or brokerage.