"How do you spell that word?"
Translation:Conas a litríonn tú an focal sin?
But in the natural interpretation of this sentence in English, "you" is a generic subject; it could be rephrased using "one", or the passive voice.
Does Irish also have a generic sense of "tú"? If not, then while using tú should still be accepted (since the English could be interpreted as "How do you spell it?"), it shouldn't be the preferred translation.
No. If you left out the tú, then an focal sin would become the subject of the verb - "how does that word spell", without any object.
Instead, you would use the saorbhriathar or autonomous form of the verb, in which the actor in the sentence is not expressed - Conas a litrítear an focal sin?, which is usually translated with the English passive sentence "How is that word spelled?"
The saorbhriathar or "autonomous" is used in Irish where you use the passive voice in English to avoid identifying the "actor":
"it's spelled with a double s" - litrítear é le dhá s
"it's spelt with an 'i'" - litrítear é le 'i'
litrítear é le dhá s is in the active voice.