Given the full plate of armor was heavy and did the job of protecting the knight, would he even need a shield. Of course we are talking over a large period of time in history here but how common was it to see a knight using a shield if he was wearing a full plate of armor ?
Ho there, traveler, greetings and well met!
By full plate, I presume you mean something resembling a 'Maximilian plate'? (sample: https://en.wikipedia.org/wiki/Maximilian_armour)
Keep in mind. Those things only existed in a relatively small part of history.
Anyways, while you wait for a deeper response from a qualified historian, kindly check out this thread from our lovely FAQ regarding the effectiveness of plate armor, which I believe answer your question somewhat, if only as a sidenote.
https://www.reddit.com/r/AskHistorians/comments/1w4gbt/why_did_knights_still_use_swords_after_the/
Pinging /u/MI13.
If you desire more information, kindly check out this section in our FAQ, which might be of great interest to you.
https://www.reddit.com/r/AskHistorians/wiki/faq/militaryhistory/medievalwar#wiki_armour
Cheers.