Who was the attacker targeting in episode 1?
Who was the attacker targeting in Episode 1? No one in particular, the attacker was just a random criminal. In the light novel,


  the man had 'a backpack in one hand and a kitchen knife in the other.' After Satoru was stabbed, as stated in the light novel, the man  ran off shouting:  “Get the hell outta my way!” (Volume 1).


While the man was made to look like just a random guy sprinting in to attack Satoru in the anime, the light novel was more specific. From this, it can be said that the man is a criminal or a thief (as he has a backpack but is not wearing it over his back, which he probably stole hurriedly). Also, the man yelled to get out of his way, meaning he was in a hurry trying to get away from someone or something. 

The wiki synopsis also states that the man is a robber.