I think this is not achievable via Siri, but you can still use Siri and a couple of taps to get what you're asking for.
"Hey Siri, where am I?"
All you have to do to Mark your current location, using Siri, is following these few simple steps:
- Ask Siri "Where am I?" or similar questions;
- It will pop you up a preview of your location in Maps, tap on that preview to get into it;
- Tap the blue circle (which represents you) and tap on Mark my location.
That's it, if you want to use Siri and a shortcut to get in Maps at your current location, this are the steps to follow.
In case you would prefer to directly share your location, you'll want to follow the same exact steps, except the last one, where you'll have to Tap on Share my location, rather than on Mark my location, and that's it.
Hope this helped you out!