If my opponent makes me play a unit to a battlefield with Bone Skewer, am I attacking?

No, you are not attacking.

According to RiftJudge FAQ #9997 and FAQ #9883, units are only designated as "attackers" or "defenders" during Combat. When an effect (like Bone Skewer) moves a unit or forces a player to play a unit to a battlefield, it does not automatically make that unit an "attacking unit."

Here is how it works:

• Combat: Combat only occurs when units controlled by opposing players are present at the same battlefield and the location becomes "Contested" (Rule 447.1).
• The "Attacker" Designation: A unit is only designated as an "attacker" if it is part of an active Combat (Rule 437). Simply placing a unit at a battlefield, even if it creates a contested state, does not automatically grant the "Attacker" status to that unit.
• Showdowns: If the battlefield was empty and you move/play a unit there, you initiate a Showdown (Rule 429.1). A Showdown is distinct from Combat. Because no opposing unit is present, your unit is not an attacker and cannot trigger abilities that rely on "attacking."

In the specific case of Bone Skewer, it forces your opponent to play a unit to a chosen battlefield. If that battlefield already contains one of your units, the presence of opposing units will initiate Combat, and the unit that was moved/played by the effect is treated as the attacker because it moved to contest your battlefield (RiftJudge FAQ #9997). However, the player who controls the unit being moved is not the one "attacking"; the unit itself simply gains the "Attacker" designation due to the game rules governing combat initiation.