Where is the transmission solenoid on a 1997 dodge grand caravan?

The transmission solenoid(s) on a 1997 Dodge Grand Caravan are inside the transmission itself. There isn't an externally accessible solenoid like you might find on some other systems. To access them, you'd need to remove the transmission.

There are multiple solenoids within the transmission valve body. You cannot replace individual solenoids without removing the valve body, which is itself inside the transmission. This is a job best left to a transmission specialist or someone with considerable experience working on automatic transmissions.