Since your post says "two way radio" and not a scanner, I'm assuming this radio can transmit and isn't just a receiver?
If this is for a radio that will transmit, then no, you'll need to get an antenna that's resonant on whatever frequency you're using. If you can provide more info as to the make and model of the radio and what frequency you're using, we can provide more information on suggested antennas.
If this is for receive only, then you can use it but it may or may not work very well. Depends on what you're trying to pick up. If the radio is receive only, give it a try and see how well it receives. However, even for a receive-only antenna, it's still best to have an antenna that's resonant on the frequency you're listening on.
Well you could...but I would recommend that you don't.
The most important thing is the fact that CB operates on 27Mhz
while most trunked radio systems are on 800Mhz.
That is a horrible mismatch of epic proportions.
Buy an 800Mhz antenna designed to work with your Trunked Radio and
save yourself grief.