How do I create a autonumber field in a make table query.
You can't.
Create the table, empty, in the Tables window, and run an Append query
to populate it.
Note that MakeTable queries are VERY rarely really necessary; in a
properly normalized database there will already be a table for each
Entity represented by your database. If you're creating a table on the
assumption that you need a new table every time you have a new set of
data to report (or export), reconsider that assumption; it's easier to
base Forms, Reports, and file exports on a Select query than it is to
change the exact same select query into a MakeTable query.
John W. Vinson[MVP]