What should we enter in Payer's TIN box if pension is from foreign country?

It depends. In this Turbo Tax support article, it mentions to use 99-0999999, which has worked in the past. I have heard occasionally that it doesn't work or may work for some and not for others. This would be the first option that you may try. It may be rejected however because the IRS may reject your return electronically because it isn't a valid TIN for US tax reporting purposes.

A second option would be to prepare the return and leave the tin blank.  This is a wonderful option except you will not be able to file electronically because there is no TIN listed in the payer's ID section.

A third option would be to report this income as other miscellaneous income. This would be perfectly acceptable as you would list it as a foreign pension.  Here is how to report this.

1. Log into your account
2. Select Wages and income
3. Less Common income
4. Miscellaneous Income, 1099-A, 1099>start
5. Scroll to the bottom of the page to Other Reportable Income
6. Other taxable income, answer yes
7. Then give a brief description of the income and the amount listed..

Here, describe the income as Foreign Pension Income and the amount of the pension income.