Something like this? I'd recommend adding a WHERE clause to quicken the query results
SELECT TalkInTime, TalkOutTime, TalkOtherTime, TalkAutoOutTime, TalkPreviewTime, TalkReserveTime, LoggedOnTime,
(COUNT(TalkInTime + TalkOutTime + TalkOtherTime + TalkAutoOutTime + TalkPreviewTime + TalkReserveTime)
/(SELECT LoggedOnTime FROM Agent_Skill_Group_Interval)) AS PercentageActive
FROM Agent_Skill_Group_Interval
GROUP BY TalkInTime, TalkOutTime, TalkOtherTime, TalkAutoOutTime, TalkPreviewTime, TalkReserveTime, LoggedOnTime