How To Start In A New Role As Business Analyst?

An expert SME has been supporting various applications, I now have to fill his role and conduct all the business analyst and related business support tasks.

Does anyone have any tips as to important questions to ask or where I can find any?

Besides finding out who he has been dealing with and getting him to give his knowledge to me (good luck) , explain system process.

I don’t have any structured approach at this point.

Additionally, I am concerned I won’t get much information from him and I could be left holding the bag in this role without any training or information….