What to write if middle name is dela Cruz?

if small d and capital L as in de Leon, your middle initial is L.

if Capital D as in De leon or adjuncted as in Deleon then middle initial is D.

if both are in capitals,k as in De Leon then use D.G.

this confusion stemmed from adapting old spanish rules with regards to the use of middle names to our current use of the english rules in the usage of middle initials.

-from pinoyexchange.com