3DS XL does not have a second Circle Pad. Not yet, at least.
Nintendo will be offering a 3DS XL version of the Circle Pad Pro some time this year. The company revealed plans for the accessory in a Q&A about the 3DS XL that appeared in Famitsu this week (you can view a sample page from the Q&A at Famitsu.com).
They couldn't have just added a second circle-pad to the XL to begin with? Fucking Nintendo.