If you want to know the location it was referenced from, you'd have to open the .csproj file in a text editor and look for the HintPath for that assembly - the IDE for some reason does not show this information.
If you want to know the location it was referenced from, you'd have to open the .csproj file in a text editor and look for the HintPath for that assembly - the IDE for some reason does not show this information.