Determine which trace flags are set as a startup parameter vs. enabled globally?
If you are running SQL Server 2008 R2 SP1 and up then you can query sys.dm_server_registry to find out TRACE FLAGS that are enabled at startup.

select * from sys.dm_server_registry
where 
cast(value_data  as varchar(max)) like '%-T%'




Just incase if you or future visitors need the output in one row then, you can use below T-SQL :

select distinct @@SERVERNAME as SERVER_NAME
                ,replace(STUFF((
                        select ' ' + cast(value_data as varchar(max))
                        from sys.dm_server_registry
                        where cast(value_data as varchar(max)) like '%-T%'
                        for xml PATH('') -- select it as XML
                    ), 1, 1, ' ')        -- This will remove the first character ";" from the result
        , '&amp;#x00', '')                   -- This will remove the "&amp;#x00" else you will get  -traceFlag&amp;#x00
    as TRACE_FLAGS_ENABLED_AT_STARTUP
from sys.dm_server_registry
where cast(value_data as varchar(max)) like '%-T%'