The usual case is that you have a (possibly complex) formula with double quotes in it and you know it works, but just want to have VBA drop it into a cell, using:
ThisWorkbook.Sheets("MySheet").Range("A1").Formula = "=TheFormulaWithCHR(34)substituted in for the double quotes"
The easy way to create is to take the formula you have with the double quotes and use Find/replace in Notepad or a similar basic test editor:
Find
"
Replace with
" & CHR(34) & "
and you will then have a working formula. That's much easier than rebuilding the original formula to use CHR(34) manually, particularly if it's an expression incorporating several double quotes. To tidy up instances where the original formula had two double quotes together:
Find
& "" &
Replace with
&
It obvs doesn't matter if you CONCAT an empty string into the expression - your formula will work regardless - but it's tidier not to. Two Find/Replace operations, job done.