"Where is the plate that I was eating from?"

Translation: Kde je ten talíř, z něhož jsem jedl?

[JamesTWils]

Is that either feminine or masculine?

[VladaFu]

talíř? definitely masculine (ten, z něhož; ten, ze kterého;...)

[Alex.Eisner]

I'm confused about the case here. The word tiles gave me "z nějž" which suggests accusative but thats certainly wrong, as im not asking where the plate i was EATING is currently.

[VladaFu]

z always uses genitive