Story of the match
The visitors' best chance came just before half-time after a shambolic mix-up between Westwood and Adam Reach.
Westwood's poor ball out wide was headed back towards him by Reach, and the Owls keeper conceded a penalty after bringing down Knockaert.
But Westwood redeemed himself as he dived the right way and saved Grabban's spot-kick.
Grabban rounded Westwood early in the second half after a sloppy back pass by Julian Borner but could only hit the side netting from a tight angle.
Wednesday introduced Jordan Rhodes in the 56th minute as the search for the opener continued.
The 31-year-old had a chance soon after but could only direct his header straight into the arms of Samba.
He missed the target from another headed chance seven minutes later after being found by Windass at the back post.
Windass then tried to beat Samba at his near post, but the Forest shot-stopper was equal to it.
The Owls had opportunities to win it late on, with Rhodes and Borner heading straight at Samba either side of a Harris free-kick that went wide.