1) Query to get the user belong to which group.
select group_name from dm_group where any i_all_users_names = 'dmadmin'
Your second question is clear to me. Are you trying to get a latest version of a document?
A regular DQL statement will always return a lastest document only.
1. select i_all_users_names from dm_group where group_name='<insert value here>' or select users_names from dm_group where group_name='<insert value here>'
Take a look at the object reference manual for dm_group for the difference in the requested data
2. select r_object_id from dm_document where i_chronicle_id='<value here>'
Queries will return the latest version by default
Thanks Andy