Google has a testing tool to check if a page is "mobile friendly". This is also part of the testing that you can perform using Google's Search Console. You can even check a web page of a site that you do not own.
Unless I make a mistake on a page and I am using the correct template all my pages should pass this test. I can check the pages on my computer by sizing the window or viewing the page on a mobile phone. I cannot check this on a tablet (iPad) as the screen resolution is too high (athough the device-width is classifid as a mobile device).
How to make a page "Mobile Friendly"
In addition to checking to see if your pages are "Mobile Friendly" there are design tips that you can follow to achieve this.