Is it permissible for me to benefit from the jewelry that caused the engagement to be broken in another engagement, and is Zakat obligatory on it, and is it permissible for me to benefit from the investment certificates saved for me?

Most common investment certificates in banks are unlawful (haram), and it is not permissible to benefit from the money generated by them. Rather, you must dispose of what you have of them by spending it on the welfare of Muslims. As for the gold you bought with these funds, you are not required to dispose of it. You may benefit from it after disposing of its unlawful price for the welfare of Muslims. This is in line with the fatwas of the Permanent Committee regarding clothes bought with unlawful money. As for the zakat on this gold, it is apparent that zakat is obligatory if it reaches the nisab and a hawl (one lunar year) has passed, because you acquired ownership of it through purchase, and the preponderant opinion is that money is not designated by specific identification.