Q.Gardenia care
How do you find out the pH level in the plant and the cloaphill level?

Certified GKH Gardening Expert
The pH can be found by either sending your soil in to be tested or by getting a home test kit, which would be available at many home and garden centers.
Chlorophyll is not something that you would test so much. That is the coloring in the plant that makes them green. If you lack certain nutrients, your plant would become less green (and less healthy).
A soil test will also tell you what nutrients are missing from the soil as well as the pH. This article has more information on soil tests:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm