The D365 Client API allows us to access the rows and columns of a sub-grid on a form (see docs for more details). The screenshot below shows an example of the sub-grid and using the Client API we can access the data in those specific columns.
This is a regular Read-Only grid that is displayed on a normal sized form when viewed on a device large enough to display the content. However, what happens when your device is only large enough to show a more compact view of the data, i.e. in a list view using a Card form.
BONUS TIP – after making my changes for my Card form and sub-grids I found that my D365 Solution would not import into my TEST environment. Fortunately, I am not alone in experiencing this problem and found my resolution here.