How many contacts are associated with each job. Your post #5 to me implies 2 contacts, opener and closer. Your post #6 refers to multiple contacts.
If the former, you don't need a join table, just have two fields containing the contactID for the opener and closer. (And I would call these fields ContactID_Open and ContactID_Close.) In this case you need two combo boxes to select the respective contacts. Your form shown in the screen shot in your earlier post shows neither.
If the latter, you will need to have the Job form containing a subform with all of the multiple contacts, each chosen via a combo box. You could have tick boxes indicating which is the opener, closer or whatever. You don't need a field in your tblJobSheet with the openedBy information. This way you can have any number of contacts associated with a Jobsheet.
In proper relational design, there should be a join table. However, if I knew there would never ever ever be more than two contacts, I would keep it simple and have the two fields in the Jobsheet table. I accept some old hands will argue with my "keep it simple" approach.
And either way, you still need the functionality to add new contacts. This can be done either before a new Jobsheet record is added or through the NotInList vba event.