SELECT
    *
FROM
    sysusers
;

SELECT
    *
FROM
    sysusers
WHERE
    hasdbaccess = 1;

SELECT
    *
FROM
    sysusers
;

SELECT database_id,
    name,
    collation_name,
    user_access,
    is_read_only
FROM sys.databases;

While connected to a database and using master

SELECT *
FROM sys.event_log;

SELECT * 
FROM 
    sys.event_log 
WHERE start_time>DateAdd(HOUR, -1, CONVERT(datetime2,SYSDATETIME()));

SELECT * 
FROM 
    sys.event_log 
WHERE event_subtype_desc <> 'connection_successful';