\dX

Lists extended statistics. If pattern is specified, only those extended statistics whose names match the pattern are listed. If x is appended to the command name, the results are displayed in expanded mode.

The status of each kind of extended statistics is shown in a column named after its statistic kind (e.g. Ndistinct). defined means that it was requested when creating the statistics, and NULL means it wasn't requested. You can use pg_stats_ext if you'd like to know whether ANALYZE was run and statistics are available to the planner.