Hilchos Shabbos is in the Orach Chaim section of Shulchan, not Yoreh Deah, and is therefore not strictly part of smicha. Nevertheless, we do include it as an important add-on to the smicha curriculum. This is because a well grounded, accurate, and practical knowledge of Hilchos Shabbos is crucial for every Jew – and particularly for those with smicha.
To promote the end of covering ground and acquiring practical knowledge of Hilchos Shabbos, we do not delve into the Shulchan Aruch and the intricate background discussions behind the halachos. Rather we learn from a sefer called Shmirat Hashabbat, by Rabbi Shimon Gadasi (originally published in Hebrew). The book is based on the Hilchos Shabbos of the Alter Rebbe’s Shulchan Aruch Harav, and is a condensed, crystallized, and contemporary version of it.
As mentioned, the purpose of this learning is to acquire a thorough practical knowledge of Hilchos Shabbos – what may be done and how to do it, and what may not be done and how not to do it.