To add a table in the invoice report with the detailed timesheet perfomed (description, hours/days, employee) you should first create an invoice from a sale order with delivered hours/days and some recorded timesheets. From there:

- open studio invoice report 

- add a 'data table' related to 'journal entries' > timesheets :

- the name appearing in the table corresponds to the description of the timesheet (which you can rename 'description' by clicking on the field)

- drag and drop a 'field in colum' related to quantity (corresponds to the hours/days performed)

- drag and drop a 'field in column' related to employee > employee name