Hi . Where is the crankshaft position sensor located in the MB GLA250 ? Thank

The crankshaft position sensor is not a concern for you. If you want to find it, obtain a shop manual or a repair manual through a place like AllData. A better recommendation would be to seek local guidance at a shop near you that can provide a proper diagnostic test to your vehicle. Guessing at a part you don't need is not a good decision.