Does Xcode have a watch window?

Xcode Expression window

Open Debug Area via View -> Debug Area -> Activate Console (Xcode 9)

Right click -> Add Expression

Solved! Right-clicking in the local variables window brings a menu option of "Add Expression". Type your variable name and now you are watching your variable/expression.

The language of "expression" instead of the more familiar "variable" threw me quite a bit. Hard to search for a solution when I have the terminology wrong. Seems obvious now.