How to find out which cipher suites an iOS application uses?
You could install a web proxy on your router or a computer and there are even web proxies on iOS like Charles Proxy.


https://www.charlesproxy.com/


There are great tutorials on the site above using the Mac / Linux / Windows version of this to debug and investigate ios / iPhone traffic. The iOS app to run this on the device itself is here: Charles Proxy by XK72