I have eurail global pass.and I booked nightjet which directly goes to Venice from wien throngh obb website.
I paid resevertion fee which is discounted for eurail pass holder.
My eurail pass is flexible one,so I need to register travel day.
Rail planner app says there is not direct train to Venice.
how can I register travel day as 1 day？ or is it going to2 days?
There is a direct night train and since you booked a reservation, it is expected to run.
You did not mention your travel date but I see with today's date that there's a slightly faster overnight option by changing twice, and the planner is showing that, but that's not what you want. You can filter the planner for night trains or direct trains only and then you should find your night train.
Do note that you only need to add the train to your pass before boarding. There is no need or to do that a long time in advance.
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