Runes of Magic US / AU

It sounds like you are an elf. Therefore you need go to where you were ported to Varanas (if you exit class hall, bear left and go up some stairs).
Up those stairs is the elven class master.
Hope this helps.

Even as an elf, you should be able to use the class trainers in Varanas, assuming you aren't trying to pick Priest or Knight as your secondary (elves can't be these two classes). If you are looking for the elf-specific classes (druid or warden) then follow Craigers advice, you'll find those two trainers there.

Of course, you also didn't say where you were trying to look. It doesn't matter if you don't pick a class at lvl 10. I've gone to lvl 50 without picking a secondary class because I was bored at the time.

If you are in Varanas, they are all in the class hall except for the Druid and Warden ones. You can talk to all of them to get a secondary class, but of course, you can't be knight or priest if an elf, or warden or druid if a human.

Of course, if you somehow got sent to CoO, the class masters don't become available to you until you complete a quest chain. Also, once you pick up a second class, you can never complete that quest chain.