craft-imageoptimize plugin cropping position
FWIW, I would not recommend doing image resizing via your Twig templates, because it will do them on page load time. Rather, I’d recommend doing them via an Optimized Images field as per: https://github.com/nystudio107/craft-imageoptimize/blob/v1/README.md#dynamically-creating-optimized-image-variants

But if you really want to do it, the parameter there is the same as you’d use for regular Craft transforms: https://docs.craftcms.com/v3/image-transforms.html#defining-transforms-in-your-templates

So you could do 'top-center' or such

But especially since you’re just creating one image variant, there’s no real advantage to doing this via ImageOptimize in your templates. Just use a regular Craft transform. With ImageOptimize installed, the resulting image will be optimized when done via Craft transforms, too. 

The real benefit of using ImageOptimize to create image transforms is to make creating responsive image srcsets easier.