When on SSDI and lm being asked for a Employer ID Number what do l enter?

If you are being asked that question you are trying to enter your SSA1099 in the wrong place.

Do not try to enter your SSA1099  or RR1099RB as a W-2.  Go to Federal> Wages & Income>>Retirement Plans and Social Security  (SSA1099 and 1099RRB) to enter your SSA1099.

Normally, that would be your social security number

@PEK No---your employer identification number is NOT your Social Security number.  A W-2 has an employer identification number in the upper left corner--but the above user did not have a W-2 so was trying to enter a different kind of document in the wrong place in the software.