How to enable missing Tempspc column in Oracle explain plan
This TempSpc column will only be shown if Your query will need any Temporary space like if you are sorting a big chunk of records and viewing it.

If query don't need any temporary space, this column will not be shown.
This varies from explain plan of one query to another, so you will not find it in every explain plan result.

As per this Oracle Page;


  Temporary space, in bytes, used by the operation as estimated by the
  query optimizer's approach. For statements that use the rule-based
  approach, or for operations that do not use any temporary space, this
  column is null.