Their answer was that the spirit speaks to everyone differently. And we have to put forth the time and effort to distinguish that difference between the spirit and our inner thoughts. ... But what would you say to that?
Not sure if rhetorical, but let's have a go.
The truth is in the proposition. If a statement is true (objectively, for you me and everyone else in reality), then we all know it with the same ways of knowing (epistemology; how we know things).
Prayer to know... the so-called 'which Church is true' false choice? Billions of prayers point to thousands of different spiritual and religious experiences from the same method. Must not be reliable.
Next.
Prayer to... heal the blind? Take two blind girls; send one to the optometrist and the other to a worthy group of priesthood holders—one returns with contacts/glasses and the other continues with blurry vision. Prayer isn't reliable.
Next
Prayer to know... what one should or shouldn't be doing? Life's a gamble and the odds are all over the charts. How many promptings result in nothing of report? Reliability issue. How many promptings result in precisely what the odds are for any given personal experience in reality? Ask Nessy; he controls the lake, and you can know for yourself. Intro to post-hoc/ad-hoc fallacies
Prayer to... wait, is there something/someone talking to me or am I talking to myself? Welcome to Dualism; it's part of the philosophy of mind. This Yale philosophy course on death introduces the very best arguments for the possibility of anything remotely spiritual about our minds and slaughters them. Spoiler alert: The best observation and rational inference up to this point in history can't produce one shred of evidence that there's anything remotely resembling a Spirit talking to our minds.
Next
Prayer to know... well, anything about reality. If it's something objectively true, meaning it's true for me and you and everybody, we'd know by trying it out.
For example.
Pray to know a language, like BOOM, I'm fluent in French. Nope. Doesn't happen.
Or...
Pray and work hard to know a language? Nope. The MTC still churns out observably horrible foreign speakers from scratch, and they've been learning non-stop for more than two months.
Unreliable...
Pray to know (and be able to coherently demonstrate on paper) if light can travel in packets? Not a chance; gonna need lots of education. But to know if it's true? It's Einstein's proposition about photons, and it's reliably true for anyone who uses their smart phones, computers, televisions, the internet, reddit, and the very moment the save button on a reddit response is pushed; the truth is in the proposition. You're reading this, which means Einstein's proposition is true AND YOU DON'T HAVE TO UNDERSTAND IT. NO APOLOGISTS NECESSARY.
Prayer can do none of that. If it could, reliably, for everyone engaging, Apple and Microsoft, would be headquartered at BYU, and everybody using the internet would convert to Mormonism.
The truth is in the proposition and the proposition has to have a reliable way of knowing.
The most allegedly spiritual individual of modern times is purported (among those claiming) to have been Joseph Smith. Of the propositions he's made about reality, can any of them be said to be reliable?
Remember, Churches aren't things that are true; it's the culmination of their propositions—their statements and claims about reality—that can be things that are true and false.
If you've made it this far through my random and sometimes incoherent typing on the matter, I hope it's helpful.
If you already know this stuff, then you're a rockstar!