Nosepass is part of the group of Pokémon that do not evolve normally in Pokémon GO. If you are trying to get your Probopass but still don't know how to do it, your problems are over.
Probopass is one of Pokémon GO's special evolutions and is also among the best Pokémon to be used in the Great League. To get it, you'll need to be near a PokéStop equipped with a Magnetic Attract Module. Until that happens, the option to evolve will not appear for your Nosepass. Check out the image below:
Note that the "Evolve" button is not available for the Nosepass on the left, but it is for the one on the right. This is because he is next to a Magnetic Lure Module in action at a PokéStop. Also see that, in addition to using the Module, you will still have to pay 50 Nosepass Candy to get the evolution.
As with any Lure Module, Magnetic's effects are for all nearby players. So, it is not necessary for YOU to use the module, and can only approach one used by another player.
You can spot a PokéStop with Magnetic Lure Module still active on the map when the stop has metals floating like this:

After gathering the 50 Nosepass Candies and approaching a Magnetic Lure Module, you can finally get your Probopass:
How do I get a Magnetic Attract Module?
The Magnetic Lure Module is available in the Shop for 200 Coins but can also be obtained through Special Research, such as the quest "A millennial sleep (1/7)".
And how do I use an Attract Module?
To use any Lure Module, simply click on the Pokéstop (Gyms won't do) and then click on the icon highlighted in the image above. The game will show you all the Modules you have in your inventory, so just choose the one you want to use.
Other uses of the Magnetic Attract Module
In addition to enabling the evolution of Nosepass to Probopass, the Magnetic Lure Module also enables the evolution of Magneton to Magnezone and, for 30 minutes, increases the frequency of appearance of the following pokemons:
- Alolan diglett
- Alolan geodude
- magnemite
- Onix
- voltorb
- Electrabuzz
- Mareep
- Skarmory
- Nosepass
- Lairon
- Electricity
- beldum
- Shieldon
See also:
- How to evolve Combee into Vespiquen in Pokémon GO
- What are they for and how to get special items in Pokémon GO!
- How to evolve Tyrogue into Hitmonchan, Hitmonlee and Hitmontop in Pokemon GO!
- Pokemon GO: How to make every Eevee evolution!