The Catechism in Questions & Answers

408. Where can the church of Jesus Christ be experienced?

The church of Christ can be experienced wherever oneness, holiness, universality, and apostolicity—albeit to varying degrees—are present.
The church of Christ is most clearly revealed where the Apostle ministry, the dispensation of the sacraments to the living and the dead, as well as the proper proclamation of the word are present. It is there that the Lord’s work of redemption is manifest, in which the bride of Christ is being prepared for the marriage in heaven.

Identifying features of the church (unity, holiness, universality, apostolicity): see Question 381. et seq. The Lord’s work of redemption: see Questions 386. and 387.