I am 68, receiving SS and a pension. If I work, do I have to pay taxes on those earnings?
If you are asking if the earnings will be subject to income taxation, the answer is yes. Whether it results in a tax liability to you on your federal or state returns requires looking at your overall income and deductions.
If you are asking your work income will make your Social Security subject to taxation (at certain levels of income you make your social security subject to taxation), then the answer is "it depends"... largely, it depends on your pension, social security, and other income.