Being able to sight read chords on guitar is a very essential skill if you want to play with other musicians, but it will take some long term effort to learn. There are two main types of guitar chord sight reading that you will encounter as a player, and this article will talk about both of them.
The first type is common in pop and rock styles of music. It will most often take the form of chord names or symbols appearing above the melody or lyrics of a song. Jazz tunes will also have the harmony written above the melody in the form of chord symbols and names.
Unless otherwise specified, these chord names just mean that you have to play the given chord type on the given root note, and what voicing to use is up to you. This opens the door to some more creative chord based improvisational possibilities, but to start out, just worry about learning the names and positions of the main chords that you encounter in your style of music.
You want to be able to recognize any chord you come across by name and know where to play it, so it would be a good idea to have all of the triads and basic seventh chords down. These appear in just about every style, and should form your basic library of memorized chords.
The more difficult form of guitar sight reading of chords is when the chords are written out in notation. The reason its more difficult is that instead of having to recognize just one unit, a chord name, you have to look at a group of notes and make sense of it on the fly.
To fix this problem you must seek to make those groups of notes into one unit like the chord names are. Find some sheet music that contains many triads and work on recognizing how the different triad inversions look in notation. If you cant find suitable sheet music, write your own exercises. Once you have the triads down, move on to seventh chords and whatever other types of chords you think you need to learn.
By learning to recognize the groups of notes in a notated chord, you will condense them into single units that are easier to sight read. This will take a good deal of practice, but the ability to read through complex chord arrangements is worth it.
Guitar sight reading takes consistent, constant effort and study, but work through it one day at a time and it will come to you. In the end, along with being able to read music with other musicians, you will find your understanding of music theory and performance to be much increased.