If you're using the new expense sheet trigger in the Concur connector, you should be able to view the standard fields and custom fields in the datatree of the trigger (i.e. datatree will be visible in subsequent recipe steps).
However, if you're not seeing your custom fields, it might be because these custom fields were not configured in the Default Expense Entry type form. Workato currently pulls the custom fields out from the Expense Entry type form > Default form. For example, in the following screenshot, Project and Customer will show up as custom fields as they're found within the Default form.
If you can't view the custom fields you care about, check that:
1) the form is named exactly "Default", and
2) the fields you wish to see are within this "Default" form. If not, simply proceed to add them, then refresh your recipe schema in Workato.