String Cases Pattern Questions

Try these:

StringCases[dep, 
 "((nsubj, (" ~~ w : WordCharacter .. ~~ ", " ~~ DigitCharacter .. ~~ "))" :> w]

StringCases[dep, "(" ~~ w : WordCharacter .. ~~ ___ :> w]

{{"He"}, {"I", "he"}}

{{"wrote"}, {"read"}}

A Regex attempt:

StringCases[#, 
  RegularExpression["[(]nsubj,\s+[(]([^,]+)"] :> "$1"]&/@dep

{{He}, {I, he}}

StringCases[#, 
  RegularExpression["^[(]([^,]+)"] :> "$1"]&/@dep

{{wrote}, {read}}