Well our current interviewees are being popped into a random class for an hour or so to see if they come out smiling or running for the hills....
However (bearing in mind I've been a TA in special school for many years) I would expect:
Basic knowedge of Safeguarding... this is crucial, so have a read up of 'Saefuarding children in Education' on the .gov site. They won't expect you to quote it, but know the signs, the hot topics, what you would do in the first instance (go to the designated safeguarding lead)
Managing behaviour.. what experience you have.. maybe something like, 'a child is lying in the corridor refusing to move, what will you do?' ( answer..all positive encouragement obviously, gentle persuasion, knowedge of what motivates the child ) Sometimes just plain patience...
I was asked what I felt was the most important thing for helping children ... my answer was communcation... by whatever means a child is able.. speech, signing, PECS, augamentative communications aids... you can't learn until you have some form of communication going.
Special Schools are hard. We love the kids, but it's exhausting, often frustrating. You will most likely be whalloped or bitten at some stage .. you might be asked how you will cope with these things (ps the answer isn't 'wine' 
)
Good luck. If you end up there you will fall in love with many of the children, and also end up with a very warped sense of humour :)