Thanks both! I should have provided the context; as you point out snap download is of course the obvious way to do this.
This is on a device that has a slow connection which also drops every few minutes - meaning that it can’t download more than a couple of MB at a time. Ordinarily, snap download would still work in that case since it can resume downloads (and with your help I bent it to my will in another similar situation: Refreshing/downloading a snap over a poor connection - #8 by svet). But the version of snap installed on that device (2.21) is unfortunately too old to support download resumption - or at least it doesn’t appear to resume downloads in practice.
So my workaround to that is to download the .snap files with wget, which does support resumption of partial downloads. Now I also need to get the .assert files - hence my question.
Of course the .asset files themselves are not too large, so another viable workaround would be to run snap download on another device and then copy over the .assert files manually. But I did wonder if there’s a less convoluted way to get them, by finding out the URLs directly.
Hope that helps clarify the slightly odd question 