Tap on any verse and "Text Commentaries" in the verse tap menu.
This displays a list of available text commentaries for the verse selected. The commentaries listed will include ALL text commentaries that reference the verse that was selected. [Note: This tool is only available when your device is online.]
Just tap a text commentary title in order to read that commentator's thoughts.
When you select a text commentary, there is a quick link at the top that will take you to where the verse is referenced.
For this particular text commentary there are three references to Psalm 138:2.
In this case, the three references are all in the same section.