Nichijou fans! We had surmised that Sakamoto knows about Nano being a robot, but I was searching for explicit dialogue(s) where Sakamoto acknowledges the fact. So, after a lot of fun Nichijou research(yay), I've finally found official/"canon" evidence!!!
There is this wonderful "Nichijou web radio" album, where the two character trios, namely the Sucharaka and the Shinonome household sing about their silly daily lives. They're very catchy but I noticed something interesting in the lyrics!
Here are the lyrics at 2 minutes and 19 seconds:
In chorus: だって。。。家族{かぞく}なんだもん? | datte... kazoku nandamon?
In chorus: こども、ロボットと黒い{くろい}猫{ねこ}! | kodomo, robotto to kuroi neko!
It translates to "What even is this family? A child, a robot and a black cat!".
You can hear Sakamoto sing along.
Secondly, Sakamoto says "no comment" (literally) when Nano's raises the issue of the wind-up key on her back! I guess he finds it amusing but doesn't want to hurt Hakase's or Nano's feelings? Maybe. :P
Here are the lyrics at 2 minutes and 4 seconds:
Nano: とれないかなぁ 背中{せなか}の ネジ回し{まわし}? | torenaikanaa senaka no neji mawashi?
Hakase: かわいいのに! | kawaiinoni!
Sakamoto: 「ノー コメント」 | "no komento"
Nano's line translates to "Won't the turnkey on my back ever be removed?". Hakase reassures by saying "It's cute..." while Sakamoto says "No comment."!
By the way, I'd never have guessed I would answer my own question a year later! It was a nice assignment and a good Japanese practice! Thanks for reading, and let's hope for a season 2 of this beautiful anime! :D
P.S The song: Shinonome Kenkyuujo no, kyou mo heiwa desu.
ヾ(^∇^) Jaa, ne~