There are three books devoted to the topic of Nitel.

Mordechai Menachem Goren, Hefaru Torasecha, Ma’amar Makif miMinhag Avosanu b’Yadanu Odos Lil haAfel Nitel Nacht UMinhag Yisrael l’Vatel meEsek haTorah,[4],52, [10] pages, 2004.

This first contains a two page introduction and the next 52 pages discuss the custom, its sources, and the various opinions. The final 10 pages are some sources that are quoted in full.

[Mordechai Menachem Goren], Hefaru Torasecha, (helek bet, b’inyanei haTekufa) . . . u’Migilas Nitel, [40] pages, 2005. This is the last chapter from the prior book and discusses the tefkufa. Additionally, it includes some additional sources about nitel, quoted in their enterity and some Rabbinic statements about Jesus. The work “Megilat Nitel” is also included. This Megilah comes from the work Iggeret R. Yochonon ben Zackai, that work is discussed by Prof. Meir Bar-Ilan in an article here, where he provides, as well, a bibliography of the various editions of Iggeret R. Yochonon ben Zackai.

Yisrael Barukh Messinger, Nitel uMerosroso, Union City, NJ, 251, [4] pages, 1999.
This work is similar to the above and based substantially on Marc B. Shapiro, “Torah Study on Christmas Eve,” Journal of Jewish Thought and Philosophy 8 (1999): 319-353. At the end there is a highly charged discussion about R. Kook and Jesus in note 137 [for more on R. Kook and other controversial statements regarding Jesus, Shabbetai Zevi and others, see Bezalel Naor, Post-Sabbatian Sabbatianism (Spring Valley, NY, 1999), pp.109-13, 203-05].

In Messinger’s book he provides a bibliography of other articles that discuss the topic. One final article that is not mentioned as it came out after Messinger’s book is the chapter in R. Freund’s Moadim l’Simcha, vol. 2, pp. 397-427.