I got a response from the UCSC Genome Browser help desk which resolved my question:

The knownCanonical gene set is created from the longest transcript of the basic Gencode gene set. This convention was not around for the V23 gene set, so that file does not exist. If you would like to use a similar dataset without filtering for only the longest transcripts, you can use the Basic annotation set from Gencode V23 (http://genome.ucsc.edu/cgi-bin/hgTables?db=hg38&hgta_track=wgEncodeGencodeV23).

Alternately, you can filter out shorter transcripts, leaving the longest isoforms of each transcript by running a short script from the command line.

mysql -h genome-mysql.soe.ucsc.edu -u genome -Ne "select g.name, a.geneId, g.txEnd-g.txStart from wgEncodeGencodeBasicV23 g,
wgEncodeGencodeAttrsV23 a where g.name = a.transcriptId" hg38 | sort
-rnk 3 | awk '{if (!found[$2]) print ; found[$2] = 1}' | awk '{print $2}' > knownCanonicalV23.txt
  

The output of this script (knownCanonicalV23.txt) can be uploaded as identifier input in Table Browser. Using that file as Table Browser identifiers should allow output as if you were querying a knownCanonical data set from Gencode V23.

If you want to download a genePred file equivalent of knownCanonical for Gencode V23, you can run the following script on the command line.

mysql -h genome-mysql.soe.ucsc.edu -u genome -Ne "select   g.txEnd-g.txStart, a.geneId, g.* from wgEncodeGencodeBasicV23 g,
wgEncodeGencodeAttrsV23 a where g.name = a.transcriptId" hg38 | sort
-rn | awk '{if (!found[$2]) print ; found[$2] = 1}' | cut -f 4-  > knownCanonicalV23.gp