If you're looking for a meeting place or a good stop around ½ or halfway between Lodi and Belvedere, you can try Pittsburg, CA, which is almost an hour west of Lodi, or almost an hour east of Belvedere.
Other possible places to stop near the midpoint include Bay Point, and Clyde.
About ¼ or a fourth of the way, you can stop at Isleton, CA. This is about half an hour west of Lodi.
About ⅓ or a third of the way, you can stop at Emmaton, CA. This is about half an hour west of Lodi.
About ⅔ or two thirds of the way, you can stop at Hercules, CA. This is a little over 1 hour west of Lodi, or about half an hour northeast of Belvedere.
About ¾ or three fourths of the way, you can stop at Richmond, CA. This is about 1½ hours west of Lodi, or about half an hour northeast of Belvedere.
If you drive straight through without stopping at all, the total distance is 95 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 1 hour, 51 minutes.