Where must the donor's tax return be filed if Manolo, residing in Dagupan City, donated property located in Baguio City?

The donor's tax return must be filed in the location where the donor resides. In this scenario, because Manolo is a resident of Dagupan City, he is required to file his donor's tax return there, regardless of where the donated property is located. The tax jurisdiction for the donor typically corresponds to the donor's residency, which is why the correct choice is the location of Manolo's residence.

The other options suggest filing in the location of the property or another city, which is not the correct practice under the current tax guidelines. Tax returns for donations are administered according to the donor's residency, ensuring that the local tax authorities of that area can properly account for and handle the tax obligations arising from the donation.