Short answer. The heir to whom that specific property was adjudicated. Article 1089 of the Civil Code requires that the titles of acquisition or ownership of each property be delivered to the co-heir awarded that property in the partition, rather than being kept jointly or by whoever happened to hold them before.
What the law says
The titles of acquisition or ownership of each property shall be delivered to the co-heir to whom said property has been adjudicated.
Civil Code, Article 1089 — Delivery of Titles. Read the full provision →
The rule Article 1089 sets
Article 1089 is direct: the titles of acquisition or ownership of each property shall be delivered to the co-heir to whom said property has been adjudicated. Once the estate has been partitioned and specific properties have been assigned to specific heirs, the documents evidencing ownership of each property follow that same assignment. The heir who was awarded a particular parcel of land, or other property, is the one entitled to receive and hold the title documents for it.
Why titles follow the adjudication rather than staying together
Before partition, an estate's properties and their supporting documents are often held together as part of one undivided mass belonging to the estate as a whole. Article 1089 addresses what should happen to those documents once the properties are no longer undivided: since specific properties now belong to specific heirs, it makes sense that the paperwork proving ownership of each one should be handed over along with the actual right to that property, rather than remaining scattered among whichever heirs happened to have physical custody of them beforehand.
What this means if multiple documents cover several properties
Where a single title or document might cover more than one property that ends up being divided among different heirs, this can raise practical complications, since Article 1089 speaks of delivering titles for each property to the heir who received that property specifically. Sorting out how title documentation should be handled when properties covered by one instrument are split among different heirs is a practical matter that arises from applying this rule to real partitions, rather than something the article's text spells out in detail.
Why this matters for the heir who receives the property
For the heir who has been adjudicated a particular property, being entitled to receive its title documents under Article 1089 supports being able to deal with that property going forward, including matters like registering the transfer or otherwise establishing clear ownership. Without the underlying title actually following the property to the heir who now owns it, that heir would be left holding a right to property without possessing the documentation the law contemplates should accompany it.