Short answer. By default, the full interest the testator could dispose of in that property. A devise or legacy covers all the interest he could give, unless the will clearly shows he meant to convey less. So you take everything he had in the land, no more and no less, absent words cutting the gift down.
What the law says
Every devise or legacy shall cover all the interest which the testator could device or bequeath in the property disposed of, unless it clearly appears from the will that he intended to convey a less interest.
Civil Code, Article 794 — Extent of a Devise or Legacy. Read the full provision →
The default is everything he could give
Article 794 sets a generous baseline: every devise or legacy shall cover all the interest which the testator could device or bequeath in the property disposed of, unless it clearly appears from the will that he intended to convey a less interest. The starting assumption is that a testator who leaves you land means to give you the whole of what he held in it, not some pared-down slice. So you do not have to find special words granting "full ownership"; the full interest passes unless the will affirmatively shows he wanted to hand over less than everything he owned.
But only what he actually owned
The phrase doing the real limiting work is which the testator could device or bequeath. He can give no more than he had. If he owned the land outright, you take it outright; if he owned only a one-half share as a co-owner, the devise carries that half and not the whole parcel; if his interest was merely a usufruct or was mortgaged, you take it in that condition. The article does not enlarge the testator's holding, it passes it on as it stood. So identifying exactly what he owned at death is the first step in knowing what the devise actually delivers.
When a lesser interest is intended
A testator may deliberately give less than his full interest, and the article respects that, but it requires the intention to be clear from the will. He might leave you only the use and fruits of the land for life while the ownership goes to another, or give you the property subject to a charge, or carve out a portion. Because the default is the entire interest, anything short of it has to be spelled out; a vague or offhand phrase will not be read as cutting the gift down. If the will does not clearly reduce it, the reduction does not happen.
What to check on the ground
To know what your devise is worth, pair the words of the will with the state of the title. Establish what the testator held, sole owner, co-owner, usufructuary, and whether the property was encumbered, from the certificate of title, tax declarations and any mortgage or lease records. Then read the will for any clause narrowing the gift. Between those two, the devise's true extent becomes clear, and it is settled at probate, where the interest passing under the will is matched against the interest the testator in fact owned.