Get all current (active) subscriptions

Yeap. Just call .observers property if you is using Subject object of the rxjs package.

Hope this helps.

One of the options is to use takeUntil in combination with Subject to stop all (Observable) subscriptions.

terminator$: Subject<boolean> = new Subject();

Observable.timer(1000)
  .do(i => console.log(`timer 1: ${i}`))
  .takeUntil(terminator$)
  .subscribe();

Observable.timer(5000)
  .do(i => console.log(`timer 2: ${i}`))
  .takeUntil(terminator$)
  .subscribe();

const stopSubscriptions = () => terminator$.next(true);

I think the basic problem is that an Observable (with exception of Subject and derivatives) does not keep a reference to it's observers.

Without built-in references, you need to handle them externally in some form.

I think the best you could achieve is to create a reusable subscription 'override' to wrap the mechanism, although I doubt it's worth it.

import { Observable } from 'rxjs/Observable';
import { Subscription } from 'rxjs/Subscription';

const subscribeAndGuard = function(component, fnData, fnError = null, fnComplete = null) {

  // Define the subscription
  const sub: Subscription = this.subscribe(fnData, fnError, fnComplete);

  // Wrap component's onDestroy
  if (!component.ngOnDestroy) {
    throw new Error('To use subscribeAndGuard, the component must implement ngOnDestroy');
  }
  const saved_OnDestroy = component.ngOnDestroy;
  component.ngOnDestroy = () => {
    console.log('subscribeAndGuard.onDestroy');
    sub.unsubscribe();
    // Note: need to put original back in place
    // otherwise 'this' is undefined in component.ngOnDestroy
    component.ngOnDestroy = saved_OnDestroy;
    component.ngOnDestroy();

  };

  return sub;
};

// Create an Observable extension
Observable.prototype.subscribeAndGuard = subscribeAndGuard;

// Ref: https://www.typescriptlang.org/docs/handbook/declaration-merging.html
declare module 'rxjs/Observable' {
  interface Observable<T> {
    subscribeAndGuard: typeof subscribeAndGuard;
  }
}

Ref this question Angular/RxJs When should I unsubscribe from Subscription

I depends on whether you're using a Subject or an Observable but there's probably no way to do this "automatically".

Observables

I don't think you can have such thing as "subscribed Observable" because you either store an Observable or Subscription:

const source = Observable.of(...)
  .map(...);

const subscription = source
  .subscribe();

Here source represents an Observable and subscription represents a single subscription.

Note that you can have a Subscription instance that stores multiple other subscriptions:

const subscriptions = new Subscription();

const sub1 = Observable...subscribe();
const sub2 = Observable...subscribe();
const sub3 = Observable...subscribe();

subscriptions.add(sub1).add(sub2).add(sub3);

// Then unsubscribe all of them with a single 
subscriptions.unsubscribe();

Subjects

If you're using Subjects they do have the unsubscribe method themselves, see https://github.com/ReactiveX/rxjs/blob/master/src/Subject.ts#L96.

However be aware that this makes the Subject "stopped", for more info see https://medium.com/@martin.sikora/rxjs-subjects-and-their-internal-state-7cfdee905156