Hi,
If married filing jointly, do I check both 6a and 6b on 1040 (so as to get total of 2 exemptions)?
Does this apply if the spouse is also working and has earned income?
Thanks!

No, just pick 6b.

Such a gross error will be spotted and corrected by the IRS.

Your tax software will NOT let you pick more than one choice in block 6.

If you file as Married Filing Separately, then select only 6a. You can't claim exemption for your spouse if she has any income. Your spouse will also file her return as Married Filing Separately.

If you file as Married Filing Jointly, then select 6a and 6b. You will declare both your income and your spouse's income.

MukatA is correct, and I stand corrected. I confused the filing status (single, married filiing jointly, Head of Household, etc). Portion of the Form 1040 with the Exemption portion.