Can fusion gate activation be negated by solemn warning

1st anonymous' answer = incorrect.

Warning hits anything that includes the effect to special summon a monster

First, Warning isn't in the game.

Second, no, it cannot. Solemn Warning cannot be used against the activation of a Spell/Trap Card if it doesn't at least give you the option of Special Summoning in that same activation, e.g. Monster Reborn, or Macro Cosmos.

Since you cannot activate the effect of Fusion Gate in the same Chain Link as the card itself, Warning could not be used against it.

Solemn Warning also cannot be used against effects of Spell/Trap Cards that are already face-up on the field, or which activated in other locations, such as the Graveyard. It can only be used against monster effects and Spell/Trap Cards being played from the hand to the field, or being flipped face-up.

Only the first activation.

solemn warning isn't in the game yet and yes it can really negate anything