Knowing exactly when your labor will begin is impossible to predict. As much as you may hope to get a "sign from above" telling you that it's time, that's just not going to happen. There are, however, a few things that happen as your pregnancy comes to a close that act as your body's way of letting you know that things are progressing. You'll hear a lot of talk about your cervix "ripening" and "dilating" as you near your due date. But what exactly is that process and can you feel yourself dilate at all?
The reality is that there are very few signs of labor that you can actually feel. According to the American Pregnancy Association (APA), the most common signs of labor are lightening (the feeling of your baby "dropping" lower into your pelvis), effacement, dilation, and losing your mucus plug. Of those signs, you'll be able to feel lightening and losing your mucus plug. Unfortunately (or maybe fortunately, because it would likely feel very strange) you won't be able to feel you cervix dilate or efface.
Dilation, as defined by the aforementioned APA article, is the process of opening your cervix to allow for labor to progress and your baby to be pushed through the birth canal. It typically doesn't happen all at once though, which is likely why you can't feel it when it does happen. According to What to Expect, dilation can take weeks or it can happen overnight. The process is different for every woman.
Most women start dilating a few weeks before their baby is born. According to Belly Belly, dilation happens as a result of the mild to medium Braxton Hicks contractions that occur during your third trimester. At your final check ups, your OB-GYN will check your cervix (in exactly the way they think they will, rubber gloves and all) to tell you if you've begun to dilate and efface.
As convenient as it would be to feel your labor "coming on," knowing that your body is doing it's job and dilation will happen in its own time can be its own form of comfort as you wait for the arrival of your baby.