Hello,
Could you please provide more detail on what you are looking for.
Is it right that you watch "Biggest objects (Dominators)" view?
If so, select an object in the master (i.e. upper) table and appropriate slave view below.
In particular, "Paths" slave view which is shown by default will show paths to the selected object, which describes why the object is retained in memory. More about paths:
http://www.yourkit.com/docs/net40/help/paths.jsp
For array "new byte[50 * 1000 * 1000]" there will be no path, because it is only accessible from a local variable. Unfortunately, it's technically impossible to explicitly obtain this information. However, you can consider allocation recording feature introduced in version 4.1:
http://www.yourkit.com/dotnet/eap/
http://www.yourkit.com/docs/net41/help/allocations.jsp
It allows to learn where objects are created.
Best regards,
Anton