There is no standard report that will give you this accurately at this stage, however, you could use the Job Financial Report (under the Reports menu) and after selecting a period you could use the un-invoiced totals as your WIP (Work in Progress) figure.
Note: For the most accurate data, you'll need to ensure you have marked your selected Jobs as Invoiced. This is to ensure that you collect all the costs and time associated with the jobs you're running a report for — even costs that may still be owing.
The accuracy of this figure would depend though on how up to date your Job cards are in terms of invoicing and on Jobs where you have invoiced a Quote and not the time and materials, whether you have ensured you have Marked the Job as Invoiced, (see Options in the Job screen)
This option flags all the time and materials as invoiced and allocates them to an invoiced Quote.