This is almost certainly public domain material by now (I believe it originates in a 1906 article), but I'm happy to buy it with or without Collection of Chess Studies if I can get it as a digital download somewhere.
Nunn defers to the original analysis because of how accurate it was. The derivative material on this endgame from other authors leaves too much unanswered for a more complete understanding (the original analysis contains dozens of pages).
Troitsky's analysis of the endgame K+NN v K+P was published in the German magazine Deutsche Schachzeitung in 19 installments between 1906 and 1910. They all can be read online. I am not aware of an English translation. A Russian book featuring his full analysis was published during Troitsky's lifetime. Apart from that, I don't know of any other source.
Permalinks of the five relevant Deutsche Schachzeitung volumes follow below. In case that I missed an installment, serve yourself in the TOC at the beginning of each volume.
To access the full text you need to connect from a US IP address. If you are located elsewhere, use a VPN and set the USA as your country of origin.
Deutsche Schachzeitung 1906 (vol. 61)
permalink: https://hdl.handle.net/2027/njp.32101072325978
pages 129, 161. 193, 257
Deutsche Schachzeitung 1907 (vol. 62)
permalink: https://hdl.handle.net/2027/njp.32101072325960
pages 1, 97, 161, 225
Deutsche Schachzeitung 1908 (vol. 63)
permalink: https://hdl.handle.net/2027/uc1.a0002788768
pages 1, 101, 197, 293
Deutsche Schachzeitung 1909 (vol. 64)
permalink: https://hdl.handle.net/2027/njp.32101072325945
pages 33, 97, 161, 225, 321
Deutsche Schachzeitung 1910 (vol. 65)
permalink: https://hdl.handle.net/2027/njp.32101072325937
pages 65, 129
