You have staff who are contracted (with date ranges)

You have jobs (with date ranges)

and you want see if any staff can fulfill any jobs

Questions

Where is the relationship between staff and jobs? (or is that the contracted date range)

How do you determine whether the member of staff is qualified to do the job?

What is the maximum number of days in any date range?

Can you post ddl of the tables and what sort of output you want?