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I often use supposed to while asking questions, for example

1: Can anyone please tell me, where am I supposed to get the cab from?
instead of
Can anyone please tell me, where do/Can I get the cab from?

2: How am I supposed to get to the ballpark from here?
instead of
How do I get to the ballpark from here?

3: How am I supposed to know what values to use
instead of
How do I know what values to use.

My question is that, is using supposed to correct in these examples rather than can/do?
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1.
"Can anyone please tell me, where am I supposed to get the cab from?"
"Can anyone please tell me, where do/Can I get the cab from?"

I would say "... where should I get the cab from?"
In that sentence, supposed to implies that some external source, e.g. a person or organisation, has designated a place for you to go to, to get the cab. That is the place that you're supposed to go. It could be a taxi depot or a taxi stand. That is appropriate for this sentence. But still, I would use "where should ...". Where do ... and where can ... are also fine.

2.
"How am I supposed to get to the ballpark from here?"
"How do I get to the ballpark from here?"

The specific phrase "How am I supposed to ..." includes an implied challenge. For example, if I said "Lift this one tonne weight off the floor", you might answer "[And] How am I supposed to do that?" It's a bit like "I don't think there's any way to do that. Tell me how to do it, if you can."
So I wouldn't use supposed to with how am I, unless you want to imply that challenge.
You can use how do I (probably best), how should I, how can I, or how would I.

3.
"How am I supposed to know what values to use"
"How do I know what values to use."
Again, I wouldn't use how am I supposed to ... unless I wanted to imply a challenge. Same suggestions as for #2.
Comments  
MichealCorleoneMy question is that, is using supposed to correct in these examples rather than can/do?
Hello.

It's not a matter of whether the use is correct or not, as much as it's a matter of it being appropriate and/or suitable.

The way I think of it, How am I supposed to may be expressive of a feeling of discontent in the speaker towards being asked or ordered to do or handle something that supposedly is known to be unattainable or hard to achieve:

How am I supposed to kill a lion with my bare hands?
How am I supposed to solve this?
How am I supposed to fly back home, with no money in my pocket to buy a ticket?

It depends on the situation/context.
 KrisBlueNZ's reply was promoted to an answer.