So just double checking the ruling on something seeing as it'll be pertinent fairly soon in an upcoming campaign. The Arcane Trickster's capstone ability lets them sneak attack with any spell that does hit point damage if the opponent is flat-footed (useful for first turn fireballs) and Icicle Dagger creates a masterwork (or +1) dagger that deals additional cold damage. If you're able to sneak attack with the dagger and your opponent is flat-footed, you DON'T get sneak attack damage twice since the spell doesn't directly deal damage, correct?
Yes that would be my interpretation also. The spell simply creates the item it doesn't directly deal damage.
On a related note, are there any spells that would actually receive the double sneak attack? I guess maybe if you had an acid flask focus for a dazing acid splash that would work, 1d3 damage with an attack roll followed by additional damage the next turn (assuming they failed the save for dazing, otherwise they likely wouldn't be flat-footed anymore and then you wouldn't get sneak attack damage added to the bonus acid damage).
Hmm actually, that wouldn't be terrible if combined with spell perfection so that it stayed a cantrip.
The icicle dagger is treated as a dagger (weapon) that does "additional cold damage." If used to Sneak Attack, the icicle dagger does (1d4 (weapon) + 1 (enhancement) + Str mod + ?d6 (Sneak Attack)) physical damage + (1 or 1d6) cold damage. The physical damage is reduced by any applicable DR and the cold damage is reduced by any applicable cold resistance.
The only way I know of to get Sneak Attack to apply to twice to the "same" attack is with an arcane archer 2+/arcane trickster 10 that Sneak Attacks with an Imbued Arrow (Sneak Attack on the arrow damage) transmitting an area damage spell (Sneak Attack on the spell damage to all in the area with Surprise Spells).
On a related note, are there any spells that would actually receive the double sneak attack? I guess maybe if you had an acid flask focus for a dazing acid splash that would work, 1d3 damage with an attack roll followed by additional damage the next turn (assuming they failed the save for dazing, otherwise they likely wouldn't be flat-footed anymore and then you wouldn't get sneak attack damage added to the bonus acid damage).
Continuing damage does not gain any additional Sneak Attack dice that applied to the initial attack.