If you're looking for a meeting place or a good stop around ½ or halfway between San Diego and Encinitas, you can try University City, CA, which is about 13 minutes north of San Diego, or about 15 minutes south of Encinitas.
Another possible place to stop near the midpoint is Sorrento.
About ¼ or a fourth of the way, you can stop at Serra Mesa, CA. This is about 6 minutes north of San Diego.
About ¾ or three fourths of the way, you can stop at Solana Beach, CA. This is about half an hour north of San Diego, or about 6 minutes south of Encinitas.
If you drive straight through without stopping at all, the total distance is 25 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 28 minutes.