How do I type in a Chinese character that I don't know how to pronounce?
With stroke method, you need to know the characters very well, which means you know how to write the character in correct order. It's hard for a non-native speaker in my opinion. 

I would suggest you use the "Trackpad Handwriting" instead.

Well, well... I tried "Trackpad Handwriting" which provided by Mac, it's SO BADLY DESIGNED. I can't even believe it's product of Apple!

Thanks for @Ming 's reminder, Trackpad Handwriting has special setting to enable features like "two fingers tap clear". Then, the UE design might not that bad. But considering it's not default options, it's still bad! Not that bad, but bad!

Alternative:

Here are some online handwriting input method for Chinese, which are more effective and convenient than Trackpad Handwriting.

https://chrome.google.com/webstore/detail/google-input-tools/mclkkofklkfljcocdinagocijmpgbhab

http://hanzi.unihan.com.cn/Qpen

http://www.yibizi.com/html5/

If you are using Chrome, then the extension provided by Google may be the best choice for you.