I had similar problem in Magento 2.3.0. In my custom theme I changed layout of catalog_product_view.xml and "Add To Wishlist" stopped showing up. Any change to the file and it wouldn't be visible. So I called it manually:
<block class="Magento\Wishlist\Block\Catalog\Product\View\AddTo\Wishlist" name="wishlist" as="wishlist" template="Magento_Wishlist::catalog/product/view/addto/wishlist.phtml"/>
Add it anywhere in the code but this will work only in "Product Details". If you want to show it in product listing use following:
<block class="Magento\Wishlist\Block\Catalog\Product\ProductList\Item\AddTo\Wishlist" name="wishlist" as="wishlist" template="Magento_Wishlist::catalog/product/list/addto/wishlist.phtml"/>
I didn't checked if this works properly in product listing but it should.