How do I find in which sheets, formulas, measurements, etc. Is used a field?
For example, where is the "CODE_ART" field used? or where was the "QTA" field used?
all depends on your app, if you are using the variables in your expression, you can see in the setting for variables, another way is, you should see in each settings of your objects: like an expression and dimensions.
I don't think you will find a way that tell you where your expression is used or not by Qlik Sense. I have saw a extension which tells you this but Qlik can't tell you this info
Use Document analyse to analyse the entire file.
I donot think you can know where a particular variable has been used. If you add tags on the time of creation of calculated dimension and measure then later you can find or categorize your Measure and Dimension by Tags. Use of Tags in very useful if we properly assign it.
Hope this helps you!