You would need to know the size of the heater kit. Should be notched out somewhere on the HP placard.
5kw, 8kw, 10, 15, 20, 25, etc.
It could also depend on the blower speed but we could assume 400cfm / ton to get you an approximate temp.
Typically auxiliary/emergency heat comes on in two or three stages on a sequencer (a fancy time delay relay). You may find that it's lukewarm for a few minutes, then warm for a few minutes, and if you leave it on for a good while, it will get hot.
Truth be told there is a huge amount of variation in what you should get, depending on a large number of variables. It's hard to say what you should see. It's easy for a technician on-site to test the heaters out electrically to make sure that all the circuits are working, though.
If it seems like the heat output isn't what it used to be, it's a common failure to lose one of the circuits in the electric heaters and have less heat output than you used to get.