Basically all ranks are given a certain number of Specials they are allowed to start with.
Number of Specialities they can start with. As well as the number they can have at max through training.
Genin: 1/2
Chuunin: 2/2
Chuunin ANBU: 2/3
Jounin: 2/3
Jounin ANBU: 2/3
S-Rank: 3/4
Sanin: 3/4
Kage: 3/4
Under the rank of Jounin, you need someone of a higher rank to teach you the speciality that you are wanting to learn.
2nd Speciality needs- Five thousand words from your own posts in a joint training session with who is teaching you.
3rd Speciality needs- Seven Thousand words from your own posts in a joint training session, or on your own depending on your rank.
4th Speciality needs- Ten Thousand Words of training over the time of an ic month.