Can you give me details about what you are looking to do? I am not sure what you are asking for.
I would like if possible, during expression editing, if I select e feature, during to scroll related expressions, show in graphic area, the selected dimension, so I can understand about the selected expression. Another question is why when I select the second feature, the expression that I'm editing, disappear, losing the formulate added. See video attached.
The issue as I see it is that it is showing object parameters and when you pick one feature and move to the next it does go away. I mocked up a similiar workflow and after I picked the first value I wanted I set the filter to all parameters and then picked the next feature and it kept the first value I picked. This will help you in the near future, but if you expect the value to stay without the extra pick I would suggest that you submit an ER to GTAC.
I have attached a movie showing what I mean
Scott is correct here... Reading the error message will help you understand the specific nature of the problem.
And for the record, this aspect of expressions (the evaluation of units) has not changed at all from NX 10. You would have gotten the exact same guidance from this exact same expression. :-)