Hello, I am just an amateur in the subject of history.
Many historian books have extended elaborations about processes concerning selections senate's members or for a caste such as equites and the election of consuls during times of Roman Republic. However, I didn't face exact information about who regulated the selection of augurs during that time. Were it elective positions? Than among whom election occurred? Was some some special sacred education is necessary for that position? Which type of a person could occupy this position? For example, if someone had occupied the position of aedilis, could he have been elected as a augur in the future?
Thank you, for your answers.
I will gladly receive any useful information about this topic.
Rome was around for a long time, and so some of the questions you have asked changed over time.
As to who could serve as an augur, it was originally an office specific to patricians, but this was later changed to allow some plebians to serve as well.
A priesthood or augury was not part of what the Romans called the cursus honorum, meaning that it did not fall in any particular sequence, unlike, for example the office of aedile that you mentioned. A great many politicians in the Roman Republic were never priests or augurs at all, and one could become a priest or augur, in theory, at any point in one's political career. Offices like augur and pontifex were very prestigious and got the holder up in front of a lot of people at a lot of public events, and so ambitious young politicians who wanted a leg up in name recognition would benefit greatly from being a priest or augur, but it was all informal.
Originally, augurs and other priests were chosen by co-optation from within their college, meaning that whenever a vacancy occurred, the remaining members of the college would select a new member. This was changed in 104 BC, when the priestly colleges were made elective (by the tribal assembly). The archconservative dictator Sulla, as part of his efforts to turn back the clock a couple of hundred years and restore senatorial supremacy, revoked the election of the priestly colleges, but like so much of the Sullan system, it didn't stick.
As for training, the most we can confidently say is that there are surviving manuals of how to do augury, and also models of livers with drawings and writing on them to explain what good and bad omens might look like. This would certainly argue that there was some sort of standardized practice of augury, but we also suspect that a lot of it was simply made up for political reasons. For example, the consul Bibulus, in order to screw over his co-consul Caesar, tried to block some of Caesar's legislation by claiming that the omens were bad (which only resulted in getting severely beaten and having feces dumped on him from a bucket).