Synthesized answer
The provided passages do not contain information about what questions remain unanswered regarding the electrical telegraph. The only passage available is a title page listing the title of a work and its author [1]. This passage does not offer any content from the book itself, and therefore cannot be used to determine any unanswered questions.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: “Der” elektrische Telegraph als deutsche Erfindung Samuel Thomas von Soemmerring's by Samuel Thomas “von” Sömmerring Pages: 26