Downloading and reading data in go
After spinning two routines main should wait for them to terminate. See sync package for common synchronisation primitives. fmt.Scanln is for input reading.
http.Get may return error. Proper way would be to handle it.
resp.Body will be closed when downloadData returns and readData won't be able to use it anymore.


Regarding your questions:


As stated by documentation resp.Body must be closed. Close it as soon as you don't need it anymore.
The code lacks error checks and proper routines synchronisation. Despite the fact this code is compiling, this is not acceptable Go code and it must be fixed.


I suggest you to read Effective Go for concurrency and error handling overview.