How can I tell if I need a better clock for my DAC?

Thanks for asking this question. I was just about to post something similar. If one has a decent CD player -- say, for example, a Rega Apollo CDP -- is jitter an issue, or is it safe to assume that the   manufacturer has dealt with this in making the one-box unit, making the transport section and DAC function together in a way that keeps jitter to a minimum?

In layman’s terms, you are referring to jitter correction. Jitter refers to the timing of the data stream (bits, or 0’s and 1’s) and insuring that they all arrive at the same time for processing. The Synchro-mesh and related products insure this correct timing plus can reject noise.

No CDP is jitter-free. The design and implementation will determine how well a standalone component or dac/transport will correct jitter. A manufacturer is also dealing with a price point of the component which includes the quality of electronics, vibration control of the transport, the power supply, and function of the laser.

Other members, including Steve N. (audioeng) can explain jitter correction in detail. Steve can explain measuring jitter since that’s what he does.
I thought I might start things off with the basics since it is complicated subject matter.

....No CDP is jitter-free...

And as you read enough on this forum you'll likely conclude that the interconnect cable between the transport and DAC also introduces jitter, and perhaps other items.

This is why I've always maintained that one must rely on their DAC to do its job and reduce or eliminate jitter given its re-clocking and/or other proprietary technology. And in this context, when I write "rely on their DAC to do its job and reduce or eliminate jitter", I don't believe this is a stretch as far as technology capabilities are concerned. This is why many DAC manufacturers proudly advertise this is what their DAC is doing, among other things. Frankly, I don't understand why there is so much hullabaloo regarding jitter. Apparently, it's as ubiquitous as air anyway so at some level you just have to live with it.