How can I take a photo with cos when I go to Comic Con alone?

First of all, if you mean communication, you can generously ask people who want to take a photo, and most people will agree, because after all, people who go spend a lot of time trying to get recognition from others, so she should be very happy that you like her cos.

Furthermore, if you mean that no one will take your picture, you can prepare a selfie stick in advance, which can be bought in many places online now.