Problem with Split-node!

How do I put SplitViewer node to effect to Composite node? There is no output in SplitViewer!

You are wanting to chain an output to an output - this is not right. You can connect composite node to the output of one or the other of your input nodes, but not to an output. If you are wanting to create an output composite of the effect you see in the split viewer, you will need to use other nodes to make a simple output look the same - I would suggest using a blend texture with a color ramp the is sharp in the middle, then using an alpha over node. You will need to fiddle about with it, but you should be able to get the kind of out put like that very easily.

you can use the translate node to a mix node to put them side by side. You’ll probably need a mask as well. See the recent post about stereoscopic rendering.