Is it permissible to agree to help an unknown person transfer a large sum of money, with a percentage of this amount for me, if there is doubt about the source of the money and that it may be money laundering for suspicious activities?

If the operation falls under money laundering, participation in it is impermissible. If its true nature is unknown, a Muslim should not expose himself to embarrassment; therefore, dealing with this person must be avoided, especially if the money left by his deceased father might involve rights for some heirs, and he intends to dispose of it without their permission.