Applying for transit visa from Indiana, USA

Hi. I am Nepalese student travelling to Nepal from USA through 2 transits in China. On my outbound flight, I have less than 24 hr stay time in China, but on my inbound flight, the stay time exceeds 24 hours. Where do I apply for a transit visa? Can I apply for it in Nepal on my way back? And do I need a single entry or a double entry visa? Thanks in advance.