There are no regulatory requirements on this other than the value of the property securing the debt may not be used in your calculation of current or reasonably expected income or assets. See the CFPB's compliance guide on QMs & ATR.
So, you just need to formulate what you think is a reasonable liquidation of the assets in question, both from a timing (when could the assets reasonably sell) and value (for how much could they be sold) standpoint, and then be able to explain it, if not defend it.
If you are also asking about asset liquidation as a source of repayment for non-QMs, there are no regulatory requirements there either. AR.