Question: I see some people point at the Sefer Torah during hagba but could not find this in halacha. Are we supposed to do it, and is there a particular finger to point with?
Answer: The Shulchan Aruch (OC 134:2) writes that when the Torah is lifted, there is a mitzva for everyone to look at it, bow down, and say vezos hatorah.. The Rema (Darchei Moshe OC 147:4) notes that this was the practice of the Maharil. The Magen Giborim (Elef Hamagen 134:7) adds that it is a mitzva to bow towards the Sefer Torah.
R’ Zvi Pesach Frank (Har Zvi OC 1:64) notes that in the tefilla of berich shemei that we say when taking the Torah out, we say ‘desagidna kamei’ meaning to bow down before the Torah. He questions why people are not particular about this halacha. He quotes the Shiltei Hagiborim (Kiddushin 14b) who writes that while it is important to stand for the Torah and those who learn it, we do not find anywhere in the Torah that people bowed to the aron hakodesh. Nonetheless, he concludes, we should follow the Shulchan Aruch and bow (See Sheyarei Knesses Hagedola YD 282).
R’ Chaim Falaji (Sefer Chaim 3:6; Lev Chaim OC 167:6) justifies the custom, explaining why it is not inappropriate to point. He does not give any source for this custom, however.
R’ Ephraim Greenblatt (Rivevos Ephraim 2:80:23; 5:215) notes that the halacha of pointing at hagba is not to be found in either the Siddur Harav or the Kitzur Shulchan Aruch Harav, etc. Nor is there any source among the classical commentaries for pointing.
In conclusion, there is no reason to point at the Sefer Torah during hagba. One should bow towards the Sefer Torah instead.