I know they're not obliged to confirm venue until 3 months before but if anyone else is anxious to know sooner rather than later where in Slovakia the game will be played, you could try sending the Slovakian FA the same email that I sent them (courtesy of google translate). No reply yet but if enough of us pester them, they might just confirm trnava as venue just to get us off their back.
To: office@futbalsfz.sk
Subject: Slovensko v Skótsko
"Vážený pán / pani,
Prosím, môžete mi povedať, kde sa bude hrať Skótsko Slovensko dňa 11. októbra 2016?
Ďakujem"