Hello,
probably the timetable is not published yet. Normaly there are direct trains every hour or more often. Due to works on the traks it could change.
Where did you try to book a reservation? Often it is better to not use Eurail/Interrail reservation service but other websites.
Padova - Verona is closed for works for 3 weeks in August. They’re connecting the new high-speed line to the old mainline. Direct trains take the long way round via the Bologna outskirts: 1h30 longer journey but definitely better than a replacement bus!
Times have just been published on trenitalia.com and they should be soon on Rail Europe/Eurail.