when filing online with turbo tax is Social Security tax, which is 12.4% in total for Social Security (and 2.9% for Medicare) automatically added

If you are referring to income from self-employment, yes if you have net income from self-employment you will owe self-employment taxes which is both the employer and employee share of Social Security taxes and Medicare taxes.

If you are an employee and receive a W-2 then the SS and Medicare taxes are withheld from your wages by your employer and reported on the W-2 in boxes 4 and 6.

You can log into your social security account any time and check your work history.  It takes a few months for the current tax year to show up. 

If you are self-employed, the SSA gets your qualifying income from line 4c of your Schedule SE provided to them by the IRS.