My favorite is the RUNQRY command. Enter it as RUNQRY QRYFILE(XYZ/tablename). It is very quick and very dirty, but it will show you everything in the table.
Or use the WRKQRY command and build a more elaborate output, screen or print. There is also SQL and other query products.
My reply above assumed you wanted to view the rows in the table. The table is an object, and a “file” in OS/400-speak, so object and file commands can be used.
Try DSPOBJD OBJ(XYZ/tablename) OBJTYPE(*FILE) (Display Object Description) to see attributes of the table which are common to all objects.
Try DSPFD FILE(XYZ/tablename) (Display File Description) to see attributes of your specific table.
Try DSPFFD FILE(XYZ/tablename) (Display File Field Description) to see attributes of the columns in the table.