In a character editor, go to Tools | Data Dictionary. Then go to Database | Reports ->. If you just want a list of the fields in a table, select Quick Field from the list of reports. If you want more detailed information on the schema definition of that table, select Detailed Table and pick your table from the list.
As Cringer indicated, you can also approach this programmatically if you like.
Code:
define variable tbl as character no-undo.
assign tbl = "customer".
display tbl label "Table".
find _File no-lock where _File._File-Name = tbl no-error.
for each _Field no-lock where _Field._File-Recid = recid(_File):
display _Field._Field-Name no-error.
end.