What is the purpose of 是 in the sentence 我是问? If it is for emphasis, I guess it would be 我是问的. What's the purpose of 是 before a verb?
我是问 (I do ask/ I am asking) is not a complete sentence.
是 before a verb phrase is for affirmation/ clarification
- I ask where is the bank
Yes, I ask where is the bank/ I did ask where is the bank (affirmation)
I am asking where is the bank (clarification) - specifically asking where is the bank, not the hospital
- I have to go to the bank
Yes, I have to go to the bank/ I do have to go to the bank (affirmation)
I am going to go to the bank (clarification) - specifically go to the bank, not the hospital
- I killed someone
- Yes, I killed someone/ I did kill someone (affirmation)
- I did kill a dog, not a person (clarification)
If you mean "唯我是问" the explanation is here:
"是" is the indicator of inverted structure. The existence of "是" indicates that the words are not in ordinary order. "是" its self does not have any meaning. To rephrase the words in ordinary order, it is "唯问我". Which means, "question me only." It is used to show responsibility. Like, if anything goes wrong, don't ask others; ask me, I take all responsibilities for this.
- (对某人)唯命是从：唯从命：follow all orders (of someone)
- 马首是瞻：瞻马首：behold the head of the horse (horse of the military leader), which means following a military leader.