Is it permissible to marry the daughter of one's maternal uncle's daughter, if the girl's mother breastfed the questioner as an infant with a suckling that he is unsure reached his stomach, and is it necessary to inform the girl of this if the marriage is permissible?

Prohibition is not established with doubt regarding the origin of breastfeeding or its number. If you doubt whether breastfeeding occurred at all from your maternal uncle's wife, or if you are certain it occurred but was less than five full, satisfying breastfeeds, then the prohibition is not established. In this case, it is permissible for you to marry your maternal uncle's granddaughter, and you are not required to inform her of this.