When Dogmeat dies, Gift of Immortality triggers, returning Dogmeat to the battlefield from your graveyard.
When Dogmeat enters the battlefield, its first ability triggers, causing you to mill five cards and return Gift of Immortality to your hand from your graveyard.
Cast Gift of Immortality by paying ({W} magic symbol) due to Semblance Anvil, attaching it to Dogmeat.