Upon joining a channel, eggdrop issues a "WHO #channel" command, and builds a channel-members list from the output. This will furthermore be updated upon seing people joining, parting and quitting. To see the current status of this list, you could use the ".channel #channel" partyline command, which will also display details such as whom people were identified (if known), jointime/idletime, and so on.
botonchan is known to fail whenever the eggdrop is excluded from the who-list, due to various server mechanics (anonymous channels, delayed join, etc).