Original Territory Management
https://releasenotes.docs.salesforce.com/en-us/winter20/release-notes/rn_sales_other_changes_territory_management_retirement.htm
Where: This change applies to Salesforce Classic in Performance and Developer editions and in Enterprise and Unlimited editions with the Sales Cloud.
How: Review our documentation and follow the instructions for setting up Enterprise Territory Management. If you use Customizable Forecasting, we also encourage you to migrate to Collaborative Forecasts.
Customizable forecasting
https://releasenotes.docs.salesforce.com/en-us/winter20/release-notes/rn_sales_other_changes_customizable_forecasting_retirement.htm
Where: This change applies to Salesforce Classic in Professional, Enterprise, Performance, Unlimited, and Developer editions.
How: Review our documentation and follow the instructions for setting up Collaborative Forecasts. If you use the original territory management feature, we also encourage you to migrate to Enterprise Territory Management.
Data.com
https://releasenotes.docs.salesforce.com/en-us/winter20/release-notes/rn_sales_datadotcom_retired.htm
Where: This change applies to Lightning Experience and Salesforce Classic.