How to return blank instead of zero?

The easiest way is probably to go to File - Options - Advanced and Uncheck "Show a zero in cells that have zero value"

But you can do it in the formula too if you like

Try
=IFERROR(1/(1/SUMIFS(Data!$E:$E,Data!$C:$C,'CG Template'!$B6,Data!$D:$D,'CG Template'!$F6,Data!$A:$A,'CG Template'!K$4,Data!$B:$B,'CG Template'!$G$3)),"")