Not sure. This looks close: https://www.etsy.com/listing/1098411564/knit-plus-size-poncho-black-gothic-cape
Nay, that's merely a poncho; a square of fabric with a hole for the head. OP image is wearing an even cloak with arm holes over an otherwise normal but all black outfit.
If you're starting out, just hit the local thrift shops, vintage stores, and discount places. Then dye things or add band patches, safety pins, chains, studs, ribbons, leather strips, etc to taste. Alt fashion respects DIY.
In the pic above, the shoes look vintage, the tights look discount store, the cape looks like something I once bought a friend at TJ Maxx, the gloves might actually be hand-made. (ask grandma to knit something for you! she'll love it!)
Maybe dark boho or boho witch/goth... Kind of feels too simple for that though (not in a bad way, just missing some details that I would look for in those)