Is there a way to find, and highlight, all locations and equations a variable is used in within a worksheet? Similar to trace dependents in Excel
No, there isn't, and if it should ever be implemented, I guess it would be in Prime, not in Mathcad 15 (or any higher). Considering the speed of development of Prime by PTC, it will be available 2 days before easter and pentecoste occur at the same date in the same year. In other words: on the celebration of St. Juttemis.
The best you get in Mathcad (15) is to (repeatedly) search for the variable name. That facility is supposed to be improved in Prime now, such that it matches the capabilities of Mathcad, with the release of Prime 6...
If you disable the definition of the variable all of the places it's used will show defaults and fails. That's a very clumsy way to do what you're asking.