What are some suggestions or ideas for a observable quantitative hypothesis people as human beings can research about?
The topic you use for this can be anything you want. The important thing to understand about this is to understand what a hypothesis is and what quantitative research means.
When you are looking at a hypothesis that means that you have posed a question about something you have observed (the research question) and the hypothesis you form will be what you expect to find as the answer to this question. For example if your question is "What weather patterns can be used to predict if it is going to rain" your hypothesis could be "If there are clouds in the sky from a low pressure front it is more likely to rain".
Quantitative research is research that is supported by data and statistical analysis to see if there is a relationship between two or more variables. To pair this with the above hypothesis you would want your hypothesis to state what the relationship between the variables being observed is expected to be, for example "There will be a positive correlation between low pressure systems and rain occurring."