Is it permissible to marry the daughter of the maternal aunt if her mother breastfed the suitor, knowing that the mother does not know the number of satisfying feedings?

If it is not established that your maternal aunt breastfed you five full, satisfying sucklings or more within the first two years of your life, then there is no state of mahramiyyah between you, and it is permissible to marry her daughter. The default is the absence of mahramiyyah, and it is not established except with certainty. If doubt arises regarding the existence of breastfeeding or its number, prohibition is not established. It is more prudent to refrain from marrying her as a precaution, because some scholars hold the view that both a little and a lot of breastfeeding establish prohibition.