It depends. Dress code for networking/career events involving the financial sector is normally "smart casual". Think casual office or smart teacher. Shirt with collar, but you don't need a tie, nor do you need to button your top button. Smart jumper will do instead of a jacket. No jeans but chinos or suit trousers. No trainers, and shoes should be polished.
Text from ds1 who is off to one tomorrow and another next week - no idea how to advise as I have no idea how these things work - is it a suit and tie thing where he will effectively be in a queue to be interviewed or just smart casual picking up info about grad schemes in a set up akin to a ucas fair?