Get basic Database Mirroring information- principal or mirror
SELECT
DB_NAME(database_id) AS 'DatabaseName'
, mirroring_role_desc
, mirroring_safety_level_desc
, mirroring_state_desc
, mirroring_safety_sequence
, mirroring_role_sequence
, mirroring_partner_instance
, mirroring_witness_name
, mirroring_witness_state_desc
, mirroring_failover_lsn
FROM sys.database_mirroring
WHERE mirroring_guid IS NOT NULL;
Also you could take help of another catalog view for the Witness server information by returing relevant descriptive session information about the witness server that you run on the witness.
SELECT
Database_name
, safety_level_desc
, safety_sequence_number
, role_sequence_number
, is_suspended
, is_suspended_sequence_number
, principal_server_name
, mirror_server_name
FROM sys.database_mirroring_witnesses;