If one accidentally ejaculates during the night, what should he do in the morning. I’ve heard things about not being allowed to pray for the whole day/week, reading Tilkun HaKlali, and immersing in a mikvah. I’ve also heard that many tum'ah laws are no longer adhered to. What is the current Jewish approach to this situation?

Today, there is no halachic significance to accidental emissions, just that one must stay away from pornography and gazing at women which may cause them, and in which case they’re not totally accidental. If it is totally accidental, than there’s nothing to feel guilty about, for it’s totally normal and an aspect of the Godly creation, eventually meant to be used as part of the creative drive to have a family. There are kabbalists who go to the mikveh or do “tikun klali” but these aren’t obligatory nor mainstream. All continue praying as usual today, since most issues of tum'a and tahara don't apply any more.