Define a viewpoint
To define a viewpoint in the URL, use the &viewpoint=cam:<coordinates> parameter.
In this example, the &viewpoint=cam:<coordinates> parameter opens the scene item b04e44630e4d4f788b4fec3f2d8c9ace at the coordinates of the Inner Alster Lake in Hamburg, Germany.
https://myportal.domain.com/portal/home/webscene/viewer.html?webscene=b04e44630e4d4f788b4fec3f2d8c9ace&viewpoint=cam:9.98717314,53.54101423,847.391;23.206,65.41
Note:
If you don't have the coordinates of the viewpoint in the scene, you can obtain them by clicking the Share button 
, unchecking the Short link box, and copying the link.
Open a slide
To open a scene to a specific slide, add the #<slide-number> parameter.
In this example, the #3 parameter opens the scene item 6c7a0d4f03d2444fb1f4fa9e85a96044 to the Hafenviertel slide in Linz, Austria, the third slide in the scene. https://myportal.domain.com/portal/home/webscene/viewer.html?webscene=6c7a0d4f03d2444fb1f4fa9e85a96044#3
Open a service by URL
If you have a URL of a service that you want to open directly in a scene, use the ?url=<service> parameter.
In this example, the ?url=<service> parameter opens a scene that loads the Portland, Oregon, building service:https://myportal.domain.com/portal/home/webscene/viewer.html?url=https://tiles.arcgis.com/tiles/P3ePLMYs2RVChkJx/arcgis/rest/services/Buildings_Portland/SceneServer
Embed minimal Scene Viewer UI
When you want to embed a scene in a third-party app, you may want a minimal Scene Viewer UI to not complicate the web page. To do this, add the &ui=min parameter.
In this example, the &ui=min parameter opens the Vancouver, Canada, scene in Scene Viewer with minimal UI:https://myportal.domain.com/portal/home/webscene/viewer.html?webscene=c7da180e4ca4414caa923d2e2724eb5c&ui=min
Use multiple parameters
To include more than one parameter, use an ampersand (&) to separate the parameters.
In this example, the & character separates the url= and the viewpoint=cam: parameters:
https://myportal.domain.com/portal/home/webscene/viewer.html?url=https://tiles.arcgis.com/tiles/P3ePLMYs2RVChkJx/arcgis/rest/services/Buildings_Portland/SceneServer&viewpoint=cam:-122.67434468,45.51190967,318.448;3.757,74.342