Server can't see animation but client can

I gather that what you’re trying to do is play an animation for potentially all clients to see when Client X does an action.

What I do when client X does an action is to call a Server RPC which then Multicast that action to all clients.

something along these lines:

ServerRPC_PickupItemAnimation_Implementation()
{
   Multicast_PickupItemAnimation()
}

... 

Multicast_PickupItemAnimation()
{
    AnimInstance->PlayAnim(...)
}

Same logic applies to blueprints. Server does not have to know about animations.
You also don’t have to pass around a reference from client to server about who does what, it knows from which specific actor instance the RPC was called.

Hope this helps.