I’m guessing from your other posts, that the frequency you want to listen to is NOT trunked.
It is simply a conventional frequency using the P25 wave form.
The EFJohnson 5100ES radios came in multiple bands, and with out knowing which specific model of radio you are looking at we can not give you an accurate answer.
My apologies. My response was to his question about trunking. I do agree with you that a non trunked system does not need a key. I should have been more perceptive.
Do you have the 5100 model number it should start with 242. You have to remove the batter to see the number. Post the entire number and I can tell you what you have.