Yes, aprx is the variable name for the current ArcGISProject object in the line of code I posted. Once you have that project, you will need to identify the Map in the project you want. If you know it by name for everyone, that's best. Otherwise, you'd have to look at all the maps to find a layer with the feature class name you want. Once you find the layer (by name) in the map of the project, step 1 I described above is complete.