The catalog of works by Bach (the Bach Werke Verzeichnis) has four appendices, Anhang I, Anhang II, Anhang III and Anhang N. The first lists the works that are known to have existed, but are either lost or survived only fragmentary. The second lists the works of which Bach’s authorship is uncertain. The third lists the works that once were attributed to Bach, but are now known to have been composed by other composers. And the fourth contains recent additions to the list.
The Trio “Herr Christ, der einig Gottes Sohn” is cataloged in the second appendice. The only known source of this work (Mus. ms. Bach P801, owned by the Staatsbibliothek Berlin) does not attribute a composer. The manuscript was written by Krebs and contains many other works that are certainly composed by Bach. So this one could well be composed by Bach as well. The style is reminiscent of the Schübler Choräle. It is very easy to imagine that the chorale is sung by a tenor with the accompaniment of a flute and basso continuo.