I'd have thought questions about how they are feeling now, coping strategies etc...
When they last had symptoms to varying degrees (eg from a bit of a wobble to not being able to cope), triggers, what helps (and what might help them in the workplace), what has changed, how they feel they can cope etc...
All sorts of scenarios so some context would help, could be from someone who is just easily stressed to someone who has had a full blown breakdown or suffering some kind of post traumatic stress. It would make a difference if any triggers were related to the workplace as to how to deal with it eg witnessing something traumatic at work or something traumatic happening versus something in their personal life or general disposition.