The ARP request is sent to which layer-2 destination addresses?

ARP request is forwarded to all the L2 addresses by using broadcast address (FF:FF:FF:FF:FF:FF) as a destination address

It is a Broadcast so it is essentially all 1.

so it is  FF:FF:FF:FF:FF:FF

Every Machine connected to network has source and destination address (physical (MAC) and logical (IP)), when a machine send a packet to a destination and packet reach to switch. Switch compare that destination address in its MAC address table if found it will send on that destination address.

If destination address not found in its MAC address table switch broadcast that packet and flooded on all ports of switch except that port on which this packet originated through this switch learn the destination MAC address and update its MAC address table and send that packet to that destination address.

arp request always will be broadcast 

ARP belongs to the OSI data link layer (Layer 2). ARP protocol is implemented by the network protocol driver. ARP packets are encapsulated by Ethernet headers and transmitted.

ARP is a broadcast message , it will spread through the LAN and blocked by the router

it will sent via bordcast  it will reach all the port available in that switch

Its is sent to a broadcast address within the same VLAN.segment