Hello DM,
Try following -
Go to table ESTMJ - Enter Material number (which you looking Specification Number) - Execute -
Copy the RECN ROOT number (from Result)
Go to table ESTRH- Enter RECNROOT number under Field RECN ROOT- execute and get the sub ID
If this process works than try in your query Joining RECNROOT for both tables and than if you still have issue than it may be missing authorization please check
Hope this helps.
Gopi