For starters, what do you want to return for this new report? Assets that don't appear in either report OR assets that appear in one report but not the other?
As for referencing a report that already exists, you can do something like this:
SELECT AssetID FROM webfubeyxtyyv6gmy00ssrhm2yjt5n1loyyw0cb7
When you open a report that already exists your URL will contain the report id, should be similar to the web[...] above.
This will run the query fresh from the referenced report and select the assetID of systems that the referenced report returns (Only works here if the referenced report also selects assetID).
Alternatively, you can create subqueries in your new report that contain the same code from your other reports.
Example:
SELECT
tblAssets.AssetID,
tblAssets.AssetName
FROM tblAssets
Where
tblAssets.AssetID in (
SELECT tblAssets.AssetID
FROM tblSoftware
INNER JOIN tblSoftwareUni ON tblSoftware.softID = tblSoftwareUni.SoftID
WHERE tblSoftwareUni.softwareName like 'java%'
)
AND tblAssets.AssetID not in (
SELECT tblAssetCustom.AssetID
FROM tblAssetCustom
WHERE tblAssetCustom.State <> 1
)
Order By tblAssets.AssetName
Or depending on your reports you might be able to combine them. I would need more info to be more specific.