You can't do it with DLookup, if I understand what you mean.  DLookup can
return only values that actually exist in the table, not values that *might*
be added if someone adds a record without specifying a value for the field.

However, you can do it using DAO:

   Me.TxtVal = _
       CurrentDb.TableDefs("tblChecks").Fields("ChkMessage").DefaultValue

Bear in mind that the DefaultValue property is a string, and will be a
zero-length string if the field doesn't have a default value.