I think that curiosity comes from appreciation. A car isn’t just a car once you understand how it works. A walk in the forest isn’t the same once you learn a bit about plants or pay attention to birdsong. Once you start sketching, art galleries come to life.
One thing I did was to have a todo list for things I don’t understand. For a while, I was reading about rainbows, doppler radars, transmissions, countries, plants etc. It might have been forced curiosity, but it planted seeds for genuine curiosity.
I have also read that sketching is the art of noticing, more so than photography. Stopping to notice things is important.
My favorite way is to find people with passions. Ask them about what their passion is! Try it, with them if possible. If you like it, you immediately have someone to share that passion with. Not only that, but they can mentor you in it, say what worked for them, where to start, etc.