What notes should I read before taking a book" a short course in general relativity" by Nightingale.

Thanks

It seems to be a fairly well reviewed introductory treatment of the subject, so the prerequisite should be just some basic knowledge of maths and physics. Most books like this are light on the maths involved and focus on a verbal explanation that might resonate with the reader. If you have above average mathematic skills, you might enjoy a more technical textbook.

The most important math background would be differential geometry.