Is the wife entitled to demand the dower in cash after having waived it, and must this amount be allocated for Hajj only?

The dower (Sadaq) is a right of the wife, ordained by God upon the man. The dower can be money, a service, or a benefit. There is no objection to a woman waiving her dower, whether before or after receiving it, provided that it is done of her own free will. If the wife forfeits her dower willingly, then the husband's obligation for it is absolved, and she is not permitted to demand it again.