When do you say Kaddish Derabanan after a shiur? What are the requirements for this Kaddish?
The following is taken from the sefer הקדיש here:
It is called Kaddish D'Rabanan because it was instituted to be said after learning Torah Sheba'al Peh which was transmitted to the Rabbis. (כנה"ג א"ח ס' קנח)
And this is what the Rambam says: Whenever there are ten or more Jews who are involved in learning Torah Sheba'al Peh, even Midrashim or Agados, when they finish one of them says standing up Kaddish D'Rabanan. (משנה תורה, סדר התפילה ל)
But only if some Aggada is said afterwards, because this Kaddish was mainly instituted for words of Aggada, and so the custom is to say after Pirkei Avos and במה מדליקין either ר' חנניא בו עקשיא or א"ר חנניא ת"ח וכו' in order that the Kaddish goes on the Aggada. (ש"ע ס' נד, מ"א, באה"ט)
And in a similar fashion even after learning Gemara or Zohar. (קשר גודל ס' ח)
The halachos of Kaddish D'Rabanan are mentioned in the Mishnah Berura in סימן נ"ד, ס"ק ט.
Many require that the shiur include words of aggadah, i.e. homiletic teachings on pesukim from Tanach. Others say kaddish after any public Torah study.
To fulfill all opinions, some congregations have the speaker say the last mishnah in Tractate Makkos (quoted below) after the shiur, so kaddish should definitely be said.
"Rabbi Chananya ben (son of) Akashya said: The Holy One, blessed be He, wanted to give Israel merit; therefore He gave them Torah and mitzvos (commandments) in abundance, as it is written: 'G-d wanted, for its [Israel's] righteousness, to make the Torah great and mighty' (Isaiah 42:21)."
What no one seems to mention is if the minyan have also to partake of the shiur. In many shuls after korbonus they have to wait for minyan and then they say kaddish immediately. Even if the chazan does say some 'agada' no one usually can hear it and certainly not understand it. Many people also dont listen to kaddish and daven away only answering the amen. This is really a kaddish l'vatolo and best left unsaid.