Hello! Is it possible to use one plugin or a plugin-combination in Sonar X1 in several softsynth-tracks at the same time (without dropping the plugin in each track)?
 
Exemple:
Softsynth 1 (Track 1): Insert Plugin Reverb
Softsynth 2 (Track 2): Insert Plugin Reverb
Instead: Plugin Reverb -> Softsynth 1/Softsynth 2 (at the same time)

One further question (perhaps a little bit complicated).
Some plugins (like guitar rig) must be defined as synth. You have to use a further midi-track to control theses plugins.
Is it possible to use these synth-plugins within several tracks at the same time?

Exemple:
Midi-Track (controls softsynth 4 Guitar Rig)
Softsynth 1 (Track 1): insert: for exemple 4 Guitar Rig
Softsynth 2 (Spur 2): -> 4 Guitar Rig (not possible)
There is a problem. You can not copy the inserted synth guitar rig, you can only drag it from one in track into the other.
But perhaps you have an idea.

Yes, use a buss. 

Put Reverb in the FX bin of a bus.  Create a new bus just for that. Call it REV.
For every channel/track that you want reverb, add a "send" on that track pointed at REV.
 
To copy a plugin from one FX bin to another (not just move it) hold the ctrl key while you drag the plugin.  You get an exact copy, including all the settings.
 
A single instance of Guitar Rig is not intended to be on more than one track at once, that would be like the whole band plugging their guitars into just one amp...  but having set up a single one, you can copy it to other tracks.