Originally occupying the touch screen on the Nintendo DS, the Pokétch (Pokémon Watch) makes a return in Pokémon Brilliant Diamond and Shining Pearl. As there's no second screen on the Switch, you'll be able to access it with the R button.
Where to get the Pokétch
Just like in the original titles, you'll find the Pokétch in Jubilife City.
Head to the Trainers School, where you'll bump into your rival. You should have a Parcel for him, given to you by his mother, so hand it over. He'll give you the Town Map in return.
Then, head into town. You'll be accosted by the boss of the Pokétch company, who asks for three coupons. There are three Clowns that have these coupons, and it's your job to find them.
Each clown will ask you a really easy question. Here's where you'll find them, and what they ask.
Clown 1: Standing outside the Pokémart
Question: Does a Pokémon grow by defeating others and gaining Exp. Points?
Clown 2: Jubilife TV Station, in front of the screen with a Clefable on it.
Question: Can a Pokémon hold an item?
Clown 3: Standing in front of the Pokétch offices.
Question: Just like Pokémon, do the moves of Pokémon also have types?
For all three Clowns, you should answer Yes.
Once you have all three coupons, return to the Pokétch boss to be given the Pokétch gadget.
How to use the Pokétch
To activate the Pokétch, press the R button. It will appear as an icon in the top right of the screen.
Press the R button again to make it larger on your screen.
To remove the Pokétch from the screen, hold the R button.
To change Pokétch Apps, press the right stick. In the Switch's portable mode, you can also use touch controls.
When you first get the Pokétch you'll only have access to four apps, but more can be obtained when advancing your adventure.