In German, there are bestimmte Artikel (definite articles) and unbestimmte Artikel (indefinite articles). For example
Er zieht den Schuh an.
refers to a specific shoe and therefore uses the definite article "der" (in the accusative form "den").
Er zieht einen Schuh an.
refers to about any shoe, not a specific one, and therefore uses ...
This has mostly been answered in the comments already, but I'll summarize and throw in my own interpretation as well. There are two things going on which might be causing the uncertainty, though the original guess is correct in that it should be ''den''.
First, ''nennen'' has an unusual valence in that it takes a subject, an accusative object, and a ...