When testing knowlidge you should ask questions like:
"How would you do ...?"
When testing experience you should ask questions like:
"Can you give me a concrete example how you dealt with ... in project .... ?"
If the candidate answers in plural form, "we did this", "we did that", ask him what his/her contribution was.
I tend to ask questions like:
"Can you explain to me how events work?"
"What is a delegate?"