if i set track 1 volume -6,4
and i wanna compensate another track for certain reason, i have to reach +6,4... sooo... can i have to put volume to +6.0, cant go higher, can i put +0.4 gain?


or to be more simple, volume +4 is it same as gain +4? tx

The difference between the 2 is the gain boosts the signal before all the fx and the volume boosts after all the fx.  I would suggest first mess with the gain then use the volume for minor adjustments

i put the normal track who was at volume -6.4 to 0, its not clipping.
but if i put this track back at -6.4 and put the master bus (its directly linked there) to volume +6.0 and gain +0.4, it begin to clip. i have to put gain to +0.3, so now its not clipping. not sure its exactly the same level at example 1... but should be really near...

It's exactly the same, if you have nothing in the fx bin. If you have a compressor or other dynamics processors in the fx bin, then they are not the same. EQs, modulators, delays, etc. don't usually care as long as the gain isn't boosting so much as to overdrive them. So yes, as far as signal levels go (assuming the fx bin is at unity, i.e. no additional gain from plugins) lowering the gain by 6.4 dB is the same as lowering it by 6 dB and then lowering it an additional 0.4 dB via the volume fader.
 
But...
 
Bear in mind that what appears on the master bus is the algebraic sum of all tracks. This means that even if no track individually exceeds 0dB, the master bus can still go over 0dB. It's a good practice to keep all your tracks below at least -6 dB. I shoot for -12 dB when I can.

what about that? 
https://www.youtube.com/watch?v=zN8nhPRsTG8
we dont really see well, but at last part, i finish with 0.3 gain on master bus, no more clipping with no fx. but 0.4 is clipping. weird!
and btw, the artifact "clipping" sound in this video is not sonar but the software i record with.

Sorry, that YouTube link's not working.

sorry and now? 
https://www.youtube.com/watch?v=zN8nhPRsTG8

cant delete post here?
ok now it work.

PsychatoR
i put the normal track who was at volume -6.4 to 0, its not clipping.
but if i put this track back at -6.4 and put the master bus (its directly linked there) to volume +6.0 and gain +0.4, it begin to clip. i have to put gain to +0.3, so now its not clipping. not sure its exactly the same level at example 1... but should be really near...

Because recordings tend to be in 24 bit, and because of Sonar's 32 or 64 bit internal processing there's so much internal digital headroom it's almost impossible to push a track (with no plugins present) into clipping, so long as the track or convertor wasn't clipping when the audio was recorded.

The master bus and the output to hardware busses are different, they will clip, as will the digital-analogue converter in the interface if it's pushed to hard. And that kind of digital clipping is the opposite of musical, it's just instant very, very loud noise. A clipping length of a few samples sounds like a click or pop, longer periods are just abrasive, grinding noise.

Once plugins are involved that can change, though plugins tend to go into an analogue-style distortion before digitally clipping, at least if they emulate anaogue hardware. So with plugins the thing to avoid is unwanted "analogue style" distortion caused by overloading the plugin's input or internal "circuitry".

There's a youtube video by James Wiltshire that's interesting concerning levels and k-metering. It focuses on Logic but it's applicable to any DAW.

https://m.youtube.com/watch?v=7WigF9IDdcQ

I'm sure Gain is post-fader and Volume is the actual prefader volume. So whatever is set on the Volume will be superceded by the gain. It really is there for you adjust output in the mix without adjusting the contrast between your other tracks. Another reason is you might be using a Direct Monitoring setup where you a +3dB difference between your input recording and playback track.
 

interpolated
I'm sure Gain is post-fader and Volume is the actual prefader volume. So whatever is set on the Volume will be superceded by the gain. It really is there for you adjust output in the mix without adjusting the contrast between your other tracks. Another reason is you might be using a Direct Monitoring setup where you a +3dB difference between your input recording and playback track.
 

You have that completely backwards. Check out page 1237 of the Sonar manual for the signal flow chart.