If someone was a guest in someone else’s home and forgot to light Shabbos candles, is there a knas?
According to most authorities, the k’nas (of lighting an extra candle) applies to the woman who forgot to light candles, even though she forgot to do so as a guest in somebody else’s house. See Iggros Moshe (Yoreh De’ah 3, no. 14, sec. 6); Be’er Moshe (8:63:2); Ashrei Ha’Ish (2:6:48, in the name of Rav Elyashiv); Rivevos Efraim (6:126:2). The k’nas applies only to the person who forgot to light, and not to other members of the household.
However, there are opinions that are lenient for a guest who forgot to light, and write that the k’nas only applies to somebody who forgot to light at home (Shevet Halevi, Kovetz Mibeis Levi 11, p. 32, note 10; see Chayei Levi 5:18:3).