Execute one of the extension commands by using the Command Palette ("View/Command Palette..." or Ctrl+Shift+P):
"fhir-resource-diagram-viewer-vscode: View the resource content as a diagram" (for viewing all attributes);
"fhir-resource-diagram-viewer-vscode: View resource references as a diagram" (for viewing the "resourceType" attribute, the "id" attribute, and attributes with references);
View the PlantUML code and diagram generated from the original content.
Notes
The extension expects the JSON representation of a resource instance's content, not its XML or Turtle versions.