In Kaddish Tiskabel, there are parts to be said (see page 131) by the congregation just before the three phrases that begin: תתקבל צלותהון, יהא שלמא, עושה שלום.
These do not appear in all siddurim and I have not observed many who say them.
What is their source?
Which traditions say them? (The link above is to a German Rite Siddur.)