Look on the bag, it should show the nutritional composition of the flour. What you are looking for is protein. If it shows 9-grams protein per 100-gram serving the protein content is 9%. If it shows something like 4-grams per serving and the serving is defined as 50-grams you would have 8% protein content.
If it doesn't have any information on nutritionals you will need to either Google the product/manufacturer or contact the manufacturer/distributor directly.
Tom Lehmann/The Dough Doctor