Pure soy protein powder is gluten-free, as it is made from soybeans that do not contain gluten protein. Gluten protein only occurs in grains like wheat, rye, and barley. However please check the ingredient list when reviewing a soy protein powder product as some additives can contain gluten.
Is your product totally gluten-free, but you still react? Soy protein powder can sometimes suffer from cross-contamination. Farmers often rotate wheat and soy fields. Crops after harvesting can also be processed and stored with the same equipment. Products can also be processed with the same equipment in factories. Cross-contamination can happen, so if you still suffer gluten symptoms after using a particular product you should try an alternative to see if the side effects cease.
Consider also that some people can have a soy intolerance in addition to problems with gluten.