My name is Alex. That can be translated in Sanskrit to mama naama alexaha (मम नाम अलेक्षः).
My name is Sita. That would be in Sanskrit. mama naama seetaa (मम नाम सीता).
If you want to ask 'what is your name' to Alex, that would be bhavataha naama kim? (भवतः नाम किम्)? the word bhavataha (भवतः) means 'your' in masculine form and the word kim (किम्) means 'what'. Similarly when you ask 'what is your name' to Sita, that would be bhavatyaaha naama kim? (भवत्याः नाम किम्)? bhavatyaaha (भवत्याः) means 'your' in feminine form.