How to monitor a job ?
which system table can be used to query the status of a JOB ( executing , executed or other ?)

I believe sysjobhistory is what you are looking for. You might also want to checkout msdb.dbo.sp_help_job if yo uwish to roll your own code.

we use something like this to display job informations

SELECT
sjv.job_id,
name = convert(varchar(100),sjv.name),
sjv.enabled,
last_run_info =
( select top 1 convert(varchar,run_status)+'*'+convert(varchar,jh ****n_Date)+'*'+convert(varchar,jh****n_time)
from msdb.dbo.sysjobhistory jh where jh.job_id=sjv.job_id and jh.step_id=0
order by run_date desc, run_time desc )
FROM msdb.dbo.sysjobs_view sjv