1)
Whatever's perfectly x is indubitably x (for example, a perfect triangle is indubitably triangular. An imperfect triangle's triangularity can be faulted/doubted/rejected)
Whatever's perfectly existing is indubitably existing.
2)
Semantically/objectively we know what's perfectly triangular (a perfect triangle)
Semantically/objectively do we know what's perfectly existing?
3)
There is nothing better than a perfect existence or a perfect being. If x is a perfect existence/being, then x exists perfectly. This is semantically/objectively contradictory to deny (just as it is semantically/objectively contradictory to deny that triangles are triangular).
4)
Do we know what a perfect existence/being is?
God (or the perfectly omnipresent. Existence is Omnipresent. God and Existence denote the same. A truly perfect being and a truly perfect existence denote the same)
Given 1-4, God indubitably exists.