My uncle was buried the first second day of Succos (on Yom Tov itself). When would the shloshim be?
The morning of 20th of Cheshvan would be the end of the shloshim. Although the shiva for a person buried on Yom Tov does not start until after Yom Tov, the shloshim starts on the day of the burial (and we only count Shemini Atzeres as one day). Therefore it stated on th 21st of Tishrei, and it ends on the 20th of Cheshvan, (November 11).
Orach Chaim 548-1, M:B 4.