EXEC msdb.sys.sp_helptext 
    @objname = N'dbo.sp_update_job';

USE msdb;
DECLARE @sql NVARCHAR(MAX);
SET @sql = N'';

SELECT  @sql = @sql + 'EXEC msdb.dbo.sp_update_job @job_name=N''' + name + ''', 
    @notify_level_eventlog=2, 
    @notify_level_email=2, 
    @notify_level_netsend=2, 
    @notify_level_page=2;
'
FROM    msdb.dbo.sysjobs;

PRINT @sql; -- << output may be truncated but EXEC will execute complete content of variable

-- uncomment to exec
--EXEC(@sql);