How can I tell if an electrical line going from an outside subpnel/breaker box to an outdoor spa blower is a 120v 0r 220v line?

The best way is to use a voltmeter to test the voltage between the contacts. There are also color codes. If it was wired correctly, the neutral should be white. That is an indication that the circuit would be a 110 V circuit. If both conductors are non-white (Black, Blue, or Red, for example), it's an indication of a 220V line.

You can also look in the panelboard and see if the line is fed by a two pole breaker.

how can i tell if an electrical line going from an outside subpnel/breaker box to an outdoor spa blower is a 120v 0r 220v line?

A tester is the ONLY way.