Is your feature request related to a problem? Please describe.
It's not really a problem. It would be just nice to have.

Describe the solution you'd like
A function like getPlayerSyncerElements that returns a table of elements (vehicles and peds) that the player is currently sycning.

Describe alternatives you've considered
When I set a player as a syncer of somthing I store that infomation and try to keep it up to date as much as possible.

If anybody is wanting something like we are talking about here you go:

function getElementsSyncedByPlayer( player,  theType )
    local elementsByType = getElementsByType( theType )
    local elementsSyncedByPlayer = {}
    for i, v in pairs(elementsByType) do
        local syncer = getElementSyncer( v )
        if syncer == player then
            table.insert( elementsSyncedByPlayer, v )
        end
    end
    return elementsSyncedByPlayer
end

This is not a nice way of doing it but it's good enough for now I guess