The most natural way to say “claim ownership” in Spanish is “reclamar la propiedad” or “reclamar la titularidad” , depending on the context.

Quick options

  • Reclamar la propiedad = to claim the property/ownership.
  • Reclamar la titularidad = to claim legal title/ownership.
  • Afirmar que es suyo / es mía / es mío = to say something is yours, in a simpler, everyday way.

Examples

  • Quiero reclamar la propiedad de la casa.
    I want to claim ownership of the house.
  • Ella reclama la titularidad del terreno.
    She is claiming title to the land.
  • Ese coche es mío.
    That car is mine.

If you want, I can also give you the best phrase for legal Spanish or the most natural everyday Spanish.