Get all business recommended fields in subgrid

How do I check if a particular field or column of a subgrid is business recommend or not? I want to do this using a web resource. Also due to some requirements, I will have to use the execution context of the form where the subgrid is present and not of the subgrid itself.

It is a little tricky because at the time that the form loads, the subgrid does not have data. So you have to use the Form's load event to attach a load event to the subgrid.

This is described in this MS Docs Page. You can do this like

function attachGridEvent(executionContext)
{
  var formContext = executionContext.getFormContext();
  var gridContext = formContext.getControl("gridCategories");

  // We have the grid, now add a "load" event handler
  gridContext.addOnLoad(MyGridLoadedEvent);
}

Now you've got a 'load' event for your grid so you can iterate through its rows and examine its data

I haven't been able to get this to work for subgrids that don't contain data

I get the first row in the sub grid. Once I have that we can loop through each of the row's attributes. Each attribute has the following methods:

getName Returns the logical name of the attribute of a selected grid row.

getRequiredLevel Returns a string value indicating whether a value for the attribute is required or recommended.

setRequiredLevel Sets whether data is required or recommended for the attribute of a selected grid row before the record can be saved.

getValue Retrieves the data value for an attribute.

setValue Sets the data value for an attribute.

MS Docs Page

I'm using some modern browser features (map, =>) but this code should work for you

function MyGridLoadedEvent(evt)
{
  var gridContext = evt.getEventSource();
  var rows = gridContext.getGrid().getRows();

  if (rows.getLength() > 0)
  {
    let rowAttributes = rows.getByIndex(0).getAttribute();
    let mappedResults = rowAttributes.map(x => x.getName() + " : " + x.getRequiredLevel());

    alert(mappedResults);
  }
}