Yellow Doll is a hybrid watermelon so any plants you grow from the seeds will not be Yellow Doll. Some plants from those seeds may be similar to Yellow Doll, others may be very different. Many hybrid watermelons produce few if any viable seeds so it is a gamble at any rate.
You can save the seeds if you like, just collect seeds from a very ripe specimen and use a strainer or piece of screen to wash them with a tiny bit of dish liquid and rinse under the tap to remove the soap and sugars. Dry them on a paper towel for a week or two before storing in a cool place out of sunlight.
If you have plenty of room and like to experiment there is nothing wrong with trying it, but if you want to be sure you have Yellow Doll next year buy seeds. You can buy seeds of non-hybrids that you can save year to year without degradation if you grow only one variety.
Decisions, decisions.