I'm sorry if it is a very basic question. But, can anyone tell me the average size (......micron) of diesel engine lubricant filter, both at a diesel car and a static engine ?

Depends on the manufacturer and if it's a full flow or bypass filter. Many diesel engines (OTR trucks and equipment) have two filters, a full flow and a bypass.

Usually replacement filters are 10 to 25 micron; you're lucky to get anything below 25 in after market, unless you go to a manufacturer with your own specs. And then you might need to specify beta or nominal ratings.
Check out Donaldson, Caterpiller, Cummins, and others for good specs.