How can I use Logos to find different variant readings in the Gospel of John? I do not want to have to count them in the NA28.
Use the textual variants section of the exegetical guide.
Use varunit:* to count them in Metzger's Textual Commentary on the GNT or the Lexham Textual Notes on the Bible. Restrict the range to John.
It will take a few minutes, but you get a count of the words involved as well as the number of passages (articles).
Where do I type this query: "varunit:*" at in Metzger's book?
Use the Search panel - Dave gave you a search argument.