Obviously, know sterile technique. Tpn's aren't that difficult, just like making a giant IV. I would know the basics of a 3 in 1 TPN, in case they decide to test you (there was someone here who said they were asked to write out a forumla for a TPN from scratch during an interview.)
Infusion, I would think they talking just about regular IV infusions or PPN's? You surely did infusions in the hospital, if you did IV's.
Intrathecal, I suppose it would be a good idea to know what medicines are commonly given intrathecally. I don't know anything about actually mixing intrathecal medicines.