You'll need to complete the cancelled debt worksheets, and if the timeshare was foreclosed upon, you will enter the value of the property. IRS Pub 4681 provides more details on what is included and excluded from income. 

https://www.irs.gov/pub/irs-pdf/p4681.pdf

For ProSeries, here is guidance: https://proconnect.intuit.com/community/help-articles/help/1040-completing-the-canceled-debt-workshe...