How to enable SQL Server Trace flags

First run query to check flag is enable or not. 

DBCC TRACESTATUS(-1)

Then execute below:-

DBCC TRACEON (1204,-1)

GO

DBCC TRACEON (4199,-1)

GO

DBCC TRACEON (2371,-1)

GO

DBCC TRACEON (3226,-1)

GO

DBCC TRACEON (1205,-1)

GO

DBCC TRACEON (1222,-1)

GO

Flag 1222 and 1204 are specially used to log deadlock errors.

Once you execute above query plz check current status to check that flags are enabled

DBCC TRACESTATUS(-1)