Legnica is a small city in southwestern Poland.
There is a small service station with a bar directly at the on-ramp of the motorway south of Legnica. If you are going from Wroclaw towards Dresden this is the last service station before the border. Since the service station is indeed very small few trucks stop here. A lot of traffic to Berlin comes through (watch out for license plates from Great Britain).
You have a bigger service station, but it is not directly at the motorway, but just hundred meters from the on-ramp where also many trucks stop. Or you can stand at the on-ramp before it turns, there is a small notch where drivers might stop. Asking at the station is probably better though.