Do you mean you aren't sure of GPL2 (the plus just means they reserve the right to change any contributed code to GPL3 or above with out getting a new license agreement from the contributer) or that you aren't sure how that interacts with a web app?

In this case, essentially all your front end code would need to be GPL2+ as well (GNU considers dynamic linking to count for GPL purposes I have a hard time imagining you could sufficiently separate the CKE code from the rest of your code/site to satisfy them). If CKE requires any server side code your back end code technically would need to be GPLed as well but you'd never have to share it (back end code is generally considered to not be distributed hence the AGPL) so it would have no real effect and no one would know if you didn't.

GPL 2+ just means you can redistribute the code under any version of the GPL from 2 or following. Your choice. At the moment there are only GPL 2 and GPL 3 but if there's ever a GPL 4 etc. those would be acceptable too.

Practically speaking, it also means that if you want to contribute code back to this code base, you would have to license your code in the same way, allowing redistribution under all GPL versions 2 and up.