Any suggestions for the best way to approach this task?

I was able to identify one Pokémon to max out just by looking at my top CP. But I’m having trouble finding two other candidates. I’ve done a bunch of searching online and didn’t really find anything helpful. The only way I’ve been able to figure to do. This is to find out whatever the max CP is for each Pokémon and then go to that Pokémon and see how far I can power it up and if it’s not as far as the max CP, I assume I’m not at the right level to be able to max it up completely? I’m not really sure how it works. All suggestions are welcomed thank you!