I would look in the Language files you are using stored in ./lang. If you are using US English then you need to edit en_US.lang.php
Try editing line 326 which should say
$strings['Bookings'] = 'Bookings';
and replace it with
$strings['Bookings'] = 'Make a Reservation';
I think that will get you what you want. The ? appears because the code is trying to find the translation of the word in the brackets in translate('this word'); Or at least I think that maybe the source of your issue
Remember to make a backup of the file you edit just in case my suggestion does not work