What is the ruling on working in an office for a commercial, non-cooperative insurance company for seven months, and what is the ruling on the salary resulting from it, knowing that this work is mandatory for the student as a graduation training and refusing it would delay graduation for a year?

The ruling on commercial insurance is prohibition (haram). Accordingly, working in its companies is forbidden due to it being cooperation in sin, unless there is a necessity for training in it and no other option is available. In such a case, there is no harm in it, nor is there any harm in taking the salary if you are in need of it. Remember that Allah is the Provider, so do not hasten to seek provision through an unlawful means.