Use advanced search, select Plus Points under upgrade type. In the subsequent search results, you can filter by available and waitlist or available only. Unless there is positive PZ space for that segment (PN for GS) then flights will show as waitlist only. If one segment of a multiple segment itin is available but not the other(s), then it will show as mixed availability. It may not make sense when you read this but it will be all be obvious in the search results.