If I notice that my friend's hair is shorter than the last time I saw the person, I want to comment on this, but I don't know how to say it Esperanto. These are some options I have thought of:
You can say:
Ĉu vi tondigis vian hararon?
Although this might seem like you are asking whether the person caused their hair to cut something, it is actually common to use -ig- with a transitive verb, and in that case the object of the new verb can refer to either the subject or the object of the original verb. So in this case tondigi hararon is technically ambiguous and could mean either that you caused the hair to be cut or that you caused the hair to cut something. However in the context it is clear that you probably don’t mean the latter. PMEG has a description of this with examples.
There are some examples of this phrase from Tekstaro:
Jen kion ni faros, Borenka: tri tagojn mi ne drinkos, por ke mia ruĝeblua vizaĝo reordiĝu, poste mi venos al vi kaj vi pruntos al mi kostumon; mi min razos, tondigos miajn harojn, poste vi veturos al ŝi kaj ŝin venigos en vian hejmon.
Tiele, la sikaj viroj malĝoje ĉesas surporti turbanon kaj unuafoje en la vivo vizitas barbirojn por fortondigi la hararon kaj barbon.
Lasi tondi strikes me as a little old fashioned, but it is not unheard of.
Tondigi is of course also possible. Actually, all your suggestions sound reasonable and I would notice anything strange about them in context. To your list I would also add Ĉu vi havas novan hararanĝon? It's what they used in Esperanto Pasporto al la Tuta Mondo
I would offer an alternative, funny as it might seem: "Ĉu vi tondiĝis?" Context is king, and since a person doesn't ever get "tondita", it's obvious that you speak about the hair. I found one occurence in the tekstaro.com, from the New Testament:
Ĉar se virino ne estas vualita, ŝi ankaŭ tondiĝu; sed se estas hontinde por virino esti kun haroj tonditaj aŭ razitaj, ŝi estu vualita.
A similar construction is used in Romanian, where that question would be "Te-ai tuns?" Explanation: "ai" is an auxiliary verb (to have) used to create the past tense "ai tuns" of the verb "(RO)a tunde=(EO)tondi". "Te" means "yourself" and is used to create reflexive verbs just like "-iĝ".
From the tekstaro:
