I've found the solution.
It's quite easier rather than i was thinking.
I'm going to illustrate it for thos who would be interessted in.
BEGIN TRAN T1
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
UPDATE [USER] SET nom = 'Vincent' WHERE id = 2
SELECT * FROM sys.dm_tran_locks
Look at the resource_description column on row where resource_type is PAGE