Judging by the Schrader valves shown on the manufacturer's web page I'm going to assume your ebike does not have tubeless tires. There may not be enough pressure left in the tube to see air escaping when the tube is still in the tire. Air coming from the spoke holes is most likely the double-walled rim filling with water and not anything to do with your flat.
To lose air there must be a puncture in the tube. While you can work on the tube with just one side of the tire removed from the rim, I find it much easier to completely remove the tube, add pressure, and check for the leak by holding the tube near my face. Sometimes the leak is so slow that I need to put the tube in water and watch for bubbles, but not normally.
Once I find the leak I mark it with a silver Sharpie and put on a patch. I pressure test patched tubes overnight and then either reassemble them into the tire or swap it with the spare tube I used to reassemble the tire earlier.
BTW - Do you carry a flat repair kit with you? I'd recommend it. I carry a spare tube, tire levers, patch kit, tire boot, mini pump & CO2 inflator, and a grease wipe. My record is 3 flats in a day, hence the spare tube and patch kit. My ebike has through axles so I also need a hex wrench to remove the wheel. This is included in the bike multi-tool I also carry.
Ride On!