The code below can be used to query the linked servers & the user assigned to it.
select s.name, p.principal_id, l.remote_name
from sys.servers s
join sys.linked_logins l
on s.server_id = l.server_id
left join sys.server_principals p
on l.local_principal_id = p.principal_id
where s.is_linked = 1
go
