شكرا is written without tashkeel and tanween
only a native or who mastered arabic can read every word without tashkeel
so basically , for me i see شكرا as شُكْراً
the ً in the last of the word it's called tanween , it's a َ (fatha ) duplicated
َ ...> ً ....> An
ُ.....>ٌ.......>Un
ِ .....>ٍ ......> In
شكراً شكرٌ شكر