What is the tin number for social security?

You are in the wrong section of the program for entering a SSA-1099 since there is no TIN for SS.

To enter Social Security benefits reported on form SSA-1099

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On Social Security (SSA-1099, RRB-1099), click the start or update button

Or enter ssa-1099 in the Search box located in the upper right of the program screen. Click on Jump to ssa-1099

Unless you work for the Social Security Administration and need to enter a W2.