simple question about sonar 8.5/X1

Sounds like you're referring to Loop Recording:

Loop Recording
When recording a vocal or an instrumental section, you might want to record several different takes so that you can choose the one you like best. You might even want to record several takes to double a part or merge the best parts of each.
Normally, to record each take you would have to arm a track, start recording, perform the take, and then stop recording. You can record multiple takes more easily using a feature called loop recording. Loop recording lets you start recording and record as many takes as you like, all in a single step.
SONAR loops between the loop start and loop end time, allowing you to record one take on each pass. SONAR creates a clip for each take. You have three choices for where these clips are stored:
●  All clips can be recorded in Sound on Sound mode and stored in a single track, where they are stacked on top of one another.
 
●  All clips can be recorded in Overwrite mode in a single track, where each take is successively muted except the last one.
 
●  Each clip can be recorded to a different track. SONAR automatically places each take into a new, empty track. No existing tracks are changed in any way.
 
When you finish recording, you can use the Edit > Undo command or CTRL+Z to erase all your takes in a single step.

then back up a couple measures, click record again, and wait until the end of the first recorded part to play the next part to be recorded, while at the same time hearing the audio from the first recorded part?

Yes, SONAR will do this with sound-on-sound record mode, placing overdubs in new layers of the same track.


Note, however, that this does not work with loop recording of audio, because SONAR will not play back the audio from preceding passes when looping. You can only hear previous takes while recording the next if you stop and start the transport in between.