Capture RDP pattern

Hello,

I am new user of wireshark. My supervisor asked me to capture the pattern of RDP using wireshark. I looked through internet and dint find any clear answer. I hope you guys would help me. This is the first time I am trying to capture any protocol pattern. I don’t know where to look for in wireshark to determine the pattern for a protocol to build a regular expression from it.
Thank you in advance.