How can I know which port a application needs to connect?

Ok guys, i have a question...

I hope im posting it in the right section.

The question its this one:

How can I know which port a application needs to connect?

I mean...i have an application and my rooter its blocking...but for unblock it i would need to know which port that application its trying to pass trought...

Thanks for the time.

Greets.

wtf is a rooter, lol

no clue due to randomness and not explained in proper english.

he means router here Try PortMon from SysInternals.com