device masking

Yup. The output will show all WWNs that may access the device, regardless of their status on the SAN and regardless of zoning. The output will show different WWN entries for different FA ports.

i mean if the result of the command is a "specific wwn "then the dev is available to the host that have the hba wwn..right?

It will simply show HBA that may see the device.
Obviously the HBA needs a zone to the specified FA port.

you may have a device that is masked, but is not mapped to an FA, obviously the host will not see it.

you may need to compare 3 commands to verify that your config is correct:
to see if device is mapped to correct FAs:

 symdev list -sid xxx | grep -w FA 

to see if the masking is correct:

 symmaskdb list database -sid xxx <-dev yyy | -wwn zzz> 

to see if the zone is correct/the correct wwn is logged in the FA:

 symmask list logins -sid xxx <-dir yyy -p zzz | -wwn aaaaaaa>