There are many different places to find data about your topic, but I suggest starting with Statista, a website which compiles data that is available from across the web.
On the Statista website, search for your topic. You should see a chart of the data and a description of where it comes from below the chart.
Statista IS NOT the source of the data. You should cite the source listed on the page.
Example: this data on public opinion in regards to gun safety and ownership comes from the Pew Research Center, so they should be cited as the source of the data. Check out the example citation below.
I've also listed a variety of topic-specific websites below that you can use to find data.