To capture this informations, use the Request Attribute feature. This feature permit a capture a lot o data from request Header, GET and POST, and more.
I hope have helped!;
The option that Joao is giving you is the only option to see the parameters in Dynatrace.
You should know before what parameter do you want to capture, so for that you have to ask to the Application Owner to provide you this info or use something like devtools from chrome to see the traffic that you are generating on the page. There is no option to see in Dynatrace all the POST parameters if you are not capture them (and it is a really bad idea capture all the parameters), that is why you need to know previously what you want to capture.