What size knitting needles are used with 12ply wool?

For 12-ply wool, which is classified as bulky or super bulky yarn, it is generally recommended to use knitting needles sized between 8mm to 12mm (US size 11 to 17). The exact needle size can vary depending on the specific project and desired fabric density, so it's a good idea to check the yarn label or do a test swatch.