As a first step, consider a calendar table with the date as datex and
startwork/stopwork times each day. Then something along the lines of

select jobid, case when startdate=enddate then endtime-starttime
else (select stopwork - starttime from calendar
        where datex=startdate) +
     (select sum(endwork-startwork) from calendar
        where datex>startdate and datex<enddate) +
     (select (endtime-startwork) from calendar
        where datex=enddate) as total_time from jobs;

Since I'm new at this you had better check it all very carefully; even
better go to an expert like Joe Celko, who sometimes answers questions
like these, but is unforgiving of mere mortals who fail to precisely
specify both the problem and ddl for its components.

could you use a calendar table? If yes, it would be very easy

Hello,

Calendar table will work. Thanks so much for your help.

Leo.