If I ask approximately one question a day (from old application exams) will it be considered flooding/spamming or is this perfectly legal?
It depends on the precise context, but generally I would say it is alright if and only if:
You make a reasonable effort to present your questions according to our guidelines. See How to ask a good question. In particular, explain the context of the question and possibly your own thoughts about it. Do not simply repost the question "as is"; this would be not well received independent of the volume.
You follow up on your posts and do not just ask it and then seem to forget about it.
In particular, combining both, take feedback you get on board. If you receive some type of complaint about one question, do try to avoid it for the next one.
It is also less of a concern when it happens over a reasonably varied selection of topics or at least in a common topic (which is likely given how you describe it).
Asking many very similar questions could raise a red flag.