How can I find the app ID for my metaobject creator extension?

[vincenz]

I have an app that creates a metaobject

It appears with the name (type) as example:

app--39503265793--my app

I have an app extension that I want to read that app type "app--39503265793--my app" 
but, I don't know the app ID.  How can I get the app ID, so I can query it?

I will query it in luquid like:

{{ app.metaobjects }}

{% for item in shop.metaobjects.app--39503265793--my app.values %}

{{ item.cart_page_message }}

{% endfor %}

but I don't know the app ID, because it will be different when installed? (I am in dev mode)

Can someone from Shopify help pls? Thanks