protected $customerSession;
protected $wishlist;

public function __construct(
    ...
    MagentoCustomerModelSession $customerSession,
    MagentoWishlistModelWishlist $wishlist,
    ...
) {
    ...
    $this->customerSession = $customerSession;
    $this->wishlist = $wishlist;
    ...
}

public function yourFunction(){
    $customer_id = $this->customerSession->getCustomer()->getId();
    $wishlist_collection = $this->wishlist->loadByCustomerId($customer_id, true)->getItemCollection();
    $product_ids = [];
    foreach ($wishlist_collection as $item) {
        $product_ids[] = $item->getProduct()->getId();
    }
    return $product_ids;
}