If a non-Jew is interested in Judaism, how should they approach commands in the Torah like Exodus 21:17, Exodus 31:14, Leviticus 20:13? Should these passages be seen not just as command not to do the prohibited things but also a command to carry out the punishment of death? After all, these commands are not "do not do this" but "if a person does this, he must be put to death." How can a non-Jew who is considering conversion justify committing themselves to a law that they consider themselves breaking if they don't, for example, stone an adulterer and adulteress?
The Torah does not command individual violence.
The penalty for individual violence is rather severe - and even if nobody got killed, the violent person would be required to pay the victim damages, embarrassment, injury, medical expenses and loss of work.
Even if the damage was unintentional, the rule is that a person is always responsible for his actions. Even when asleep, if the victim was there when he went to sleep, he is responsible for any damage he caused while asleep.
The verses quoted in the question all deal with the death sentence. The death sentence is not a commandment to individual violence, but part of civil law that a Kosher court needs to implement.
The chance of a court actually executing somebody is slim, as the requirements for a death sentence are many. For example:
Execution by a Bet Din is not applicable nowadays as we don't have anybody who qualifies to sit on a Bet Din of 23 people. (Which is why we don't have a Sanhedrin; members need the same qualifications.)
The cross-examination in a Bet Din is very strict.
The witnesses must have warned the criminal immediately before the crime that he will be killed for this act, and the criminal must have responded immediately "even though!" and then immediately have committed the crime.
- Circumstantial evidence is invalid. The witnesses have to see the entire crime being committed.
How can a non-Jew who is considering conversion justify committing themselves to a law that they consider themselves breaking if they don't, for example, stone an adulterer and adulteress?
As explained, it's not an individual's responsibility to kill anybody. Besides, a convert need not worry about [evetually, should conditions improve] being part of a Bet Din that would execute somebody, as a convert is not allowed to be a judge on a Bet Din, unless all the defendants are also converts. (Choshen Mishpat 7:1)