Take a look at the documentation here: https://docs.mendix.com/refguide7/add-date-function-calls#adddays-utc
So use the current date and add -14 days and you have the date to check on. Any date that is smaller than that date needs a notification.
So create a datetime variable and let it be this value: addDaysUTC([%BeginOfCurrentDay%],-14)
That is assuming all are UTC otherwise use the addDays instead of addDaysUTC.
You can then use a split to check $dateToCheck < $Date14Daysago