Translation:George is an amazing American professor.
I couldn't find information about the -un ending in the tips. Why does the noun and first adjective have it but the second adjective NOT have it?
There are some rules about when and when not to pronounce case endings. In spoken Arabic, people don't use them in most cases anyway. In Modern Standard Arabic (MSA) it's OK to omit the case ending at the end of a sentence (that's the case here) or in pausa.