With checkboxes on service request form, how can a user make them shown as YES when it's checked and NO when unchecked on email notification?
For the checkboxes/boolean fields, you would like the text "Yes" or "No" to be displayed appropriately for each selection within the email text.
Simplest way to do this is to use the "Drop-down selection" option on your Request Offering form.
Select the OOTB YesNo picklist for this dropdown.
Now the parameters show the text "Yes" or "No".
Otherwise, you can add expressions in your email notification to handle these type conversions.
From the Help menu: