Can I see an analog signal with changeable frequency on oscilloscope?
What, exactly, do you mean by "possible to see it on oscilloscope"? The trivial answer is yes. Just set the scope mode to single shot and trigger on a zero crossing. If you don't see the signal you're looking for, just trigger again (and, possibly, again and again. Patience is advised.)

If by "see" you mean, can you reliably trigger on the areas of interest which you have marked on your illustration? The simple answer is probably not, or at least not with your scope's built in trigger facility. There are various circuits which you could build which would do the job of providing a fairly reliable trigger, provided you have a good idea of what you're looking for. It would help if you're using a digital scope, of course, since single-shot viewing is hard without it.

In the case you've shown, where the special areas are marked by a lower frequency than the unwanted signals, you use a comparator to convert the signal to logic. You then feed this into the clock input of two retriggerable one-shots, such as an MC5438. One half has a pulse width very slightly less than the period of the desired signal, while the second has a much shorter period. The output of the first drives the reset of second. The output of the second is used as a scope trigger. This will discriminate against frequencies higher than desired.