disciple of one's disciple; grandstudent
Refers to a student of one's own student, often in traditional arts, crafts, or martial arts lineages.
The master's grandstudent presented his work for the first time.
師匠 is the master or teacher; 孫弟子 is two generations removed from the master.
Compound of 孫 (grandchild) and 弟子 (disciple), literally 'grandchild disciple'.