bu cümlelerdeki "da" hangi anlamıyla geliyor? ayrı mı yazmam lazım?

"bu sınavı kazanmamda senin büyük katkın var"
"buraya oturmamda bir sakınca var mı?"

See a translation

You typed it correctly. Only the ‘da’ meaning “too, also” is written separately.

Bu sınavı kazanmamda senin büyük katkın var. (You had a big hand in helping me pass this exam) - *in = -da

Buraya oturmamda bir sakınca var mı? (Would you mind if I sit down here?) - **we say it like ‘in sitting here’ *in = -da

*As you can see, there is no meaning for ‘too, also’ in the sentences above, therefore, you need to combine the ‘da’

*Just to give you the examples about the separated ‘da’:

Fatma da partiye geliyor. (Fatma is coming to the party too) - ‘Fatma’da’ wouldn’t be correct in this case.

Hope this helps.