When I draw from the Wondrous Item Deck of Many Things, am I and the rest of my party made aware of its effects? For example, if I draw the Rogue card, do I know that someone (currently undisclosed) now has enmity towards me?
The Deck of Many Things is a Legendary, Wondrous Magic Item.
The Arcana skill is written as follows (Emphasis Mine):
Arcana: Your Intelligence (Arcana) check measures your ability to recall lore about spells, magic items, eldritch symbols, magical traditions, the planes of existence, and the inhabitants of those planes.
You simply need to roll a knowledge check against your Arcana skill. It will be up to GM discretion whether or not the roll applies to the whole deck or to each card you draw. You will also have to talk to your GM and decide between you whether or not it is reasonable for your character to have prior knowledge of the deck given their background, as the Arcana skill states only that it allows you to recall the information, not to suddenly figure it all out on the spot.
If you decide that your character did not have reasonable prior access to this knowledge, you may be able to, at a later time, study the deck to gain this knowledge.
But, if you decide your character did indeed have prior knowledge of the deck, and you pass the roll, your character will recall the effects of the Rogue card and know that somebody is out to get you, though you don't know who.
If you fail the roll, your character draws a blank and can't remember what the card does.