Some things you just know...
The other disciples had seen Jesus after his resurrection https://www.biblegateway.com/passage...49&version=NIV
Thomas wasn't there at that time, so the other disciples told him what they had seen. However, he refused to believe it, telling them he would only believe if he saw Christ himself and the wounds in his hands and side....https://www.biblegateway.com/passage...25&version=KJV
Then Jesus appeared to him - read here https://www.biblegateway.com/passage...31&version=KJV
Blessed indeed is he who has not seen yet believes and hence the term, Doubting Thomas ....