If I had set this exercise the first thing I would question is
switch (currentPass) {
case 'monday':
At first glance that reads "switch on the current password" which is confusing as you are meant to be switching on the current day of the week so better for me would be
switch (weekDay) {
case 'monday':
Your next problem is with
console.log(weeklyPass + 'mnd');
That should be
console.log(weeklyPass + 'mndy');
The letter 'Y' is only considered to be a vowel when there is no other vowel in the syllable - "day" already has an "a" so y needs to be thought of as a consonant. If in doubt, then "y" is a consonant.