summon service

You have already engaged / paid an able, competent and intelligent lawyer who is well aware about facts of the case filed on your behalf. 

What is his / her advise  ?

It is really not possible to serve anyone in Suadi Arabia without having any address.. Just even if you involve the consulate in that reagard.

 if you can locate the address in suadi arabia you may post the sumouns trough registerd post ,however till then it is not posssible. 

Search for private detective agency and entrust this to him.  Most of the NRIs may be having at least one dependent  in India, and they may also be having properties in India.  Explore the possibility of filing RTI Application to Indian Embassy at Sauthi, and they MAY (?) give the address, as there is larger public interest involved in deserting wife and facing a trial etc.,  The process may be difficult but not impossible.

One of the most advanced IP tagging tracker apps of 2020. Through these type of apps. can find residential addresses also though out the world by any body. 

You may file the suit with the last known address. If summons could not be served, you may take steps for substituted service.