how to enable location service in android marshmallow

You need to add a dependency to your app build.gradle:

compile 'com.google.android.gms:play-services:8.1.0'

then you can use following example by calling this method:

private void displayLocationSettingsRequest(Context context) {
    GoogleApiClient googleApiClient = new GoogleApiClient.Builder(context)
            .addApi(LocationServices.API).build();
    googleApiClient.connect();

    LocationRequest locationRequest = LocationRequest.create();
    locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
    locationRequest.setInterval(10000);
    locationRequest.setFastestInterval(10000 / 2);

    LocationSettingsRequest.Builder builder = new LocationSettingsRequest.Builder().addLocationRequest(locationRequest);
    builder.setAlwaysShow(true);

    PendingResult<LocationSettingsResult> result = LocationServices.SettingsApi.checkLocationSettings(googleApiClient, builder.build());
    result.setResultCallback(new ResultCallback<LocationSettingsResult>() {
        @Override
        public void onResult(LocationSettingsResult result) {
            final Status status = result.getStatus();
            switch (status.getStatusCode()) {
                case LocationSettingsStatusCodes.SUCCESS:
                    Log.i(TAG, "All location settings are satisfied.");
                    break;
                case LocationSettingsStatusCodes.RESOLUTION_REQUIRED:
                    Log.i(TAG, "Location settings are not satisfied. Show the user a dialog to upgrade location settings ");

                    try {
                        // Show the dialog by calling startResolutionForResult(), and check the result
                        // in onActivityResult().
                        status.startResolutionForResult(MainActivity.this, REQUEST_CHECK_SETTINGS);
                    } catch (IntentSender.SendIntentException e) {
                        Log.i(TAG, "PendingIntent unable to execute request.");
                    }
                    break;
                case LocationSettingsStatusCodes.SETTINGS_CHANGE_UNAVAILABLE:
                    Log.i(TAG, "Location settings are inadequate, and cannot be fixed here. Dialog not created.");
                    break;
            }
        }
    });
}

reference link : https://github.com/googlesamples/android-play-location/blob/master/LocationSettings/app/src/main/java/com/google/android/gms/location/sample/locationsettings/MainActivity.java