The most direct way from Chongqing to Jiuzhaigou is airplane, you you should get to Chengdu first and then take the direct bus to Jiuzhaiou then. There is shuttle bus but very few between Jiuzhaigou and Huanglong. If you can not catch it, you have to make transfer at Songpan or hire a van directly. If you travel alone, better to share with fellow travelers.