For P25 trunked systems you always of course have to have the proper features in the radio.
The Astro, Astro25, and APX product lines are what will do P25.
Astro is old and obsolete. Examples would be the Astro Spectra mobile radios and Astro Saber portable radios.k
Astro 25 is previous generation, no longer sold, but still supported. That'd be XTL series mobile radios and XTS series portables.
Currrent generation is the APX series, which covers both mobile and portable radios.
Using any of them to monitor a trunked system without authorization is tricky and contains many hazards, and requires venturing into dark shadows where laws may be bent if not broken. It's also strictly for people who have prior experience with programming trunked radios and know how to avoid the inherent dangers.
Get a scanner. It's cheaper, easier, and safer.
Alternatively, you MAY be able to get permission from your system administrator to get your own radio and get it authorized on the system for very limited usage. This is not likely but you can ask if you want to.