There are little more than two months left for E3 2019, but as usual in this type of event, the publishers prepare months before the event to ensure that everything happens as planned.
In the case of Nintendo, you can check the official website with the plans for E3 2019. For now, two tournaments confirmed: the Splatoon 2 World Tournament and the 3vs3 World Super Smash Bros. Tournament. Ultimate.
It virtually guaranteed that there would be a Nintendo Direct before E3 2019 to announce news, but official confirmation is lacking. The E3 2019 will run from 11 to 15 June, so Nintendo Direct should occur before the event opens.
In previous E3 Nintendo gave a special highlight to a game. In 2016 it was The Legend of Zelda: Breath of the Wild, in 2017 it was Super Mario Odyssey, and in 2018 it was Super Smash Bros. Ultimate.
What will be the highlighted title for E3 2019? Pokémon Sword and Pokémon Shield look like good candidates.