Where I can see custom poller status

You can check CustomPollerStatistics if there are some gaps in polled data. Not sure what exactly are you looking for but the SQL can look like

SELECT n.Caption, cp.UniqueName, ca.AssignmentName,cs.DateTime

FROM CustomPollers cp JOIN CustomPollerAssignment ca ON (cp.CustomPollerID=ca.CustomPollerID)

JOIN Nodes n ON (n.NodeID=ca.NodeID)

JOIN CustomPollerStatistics cs ON (ca.CustomPollerAssignmentID=cs.CustomPollerAssignmentID)

WHERE n.IP_Address=<IP address>

AND cp.UniqueName=<poller name>

ORDER BY n.Caption, cp.UniqueName, ca.AssignmentName,cs.DateTime desc

Or you can create new Advanced Alert that will log to file when the last poll is not done in time. You have to include datetime condition in Custom SQL Alert

DATEADD(mi,<poll interval>, CustomPollerStatus.DateTime) < GETUTCDATE()