Is the electrical outlet by my kitchen sink supposed to be protected by a GFCI?
If there is an upstream GFCI device protecting that outlet it is fine. 

See if any other outlet in the kitchen has a test and reset button, when you test it and it trips does the outlet by the sink also lose power? If so then the outlet is protected by the GFCI.

The GFCI device can also be the breaker in the panel feeding the circuit. So check there as well.

If you find that they are protected by GFCI take your label printer and print out a "GFCI protected" label to put on the outlet.