with who he left vs who he left......with

[ostap77]

"Do you happen to know with who Anna left for London?"

OR

"Do you happen to know who Anna left for London with?"

Is there any tendency where to put "with" in this context?

"Do you happen to know on what floor their appartment is?"

OR

"Do you happen to know what floor their appartment is on?"

[bhaisahab]

"Do you happen to know with who Anna left for London?"

OR

"Do you happen to know who Anna left for London with?"

Is there any tendency where to put "with" in this context?

"Do you happen to know on what floor their appartment is?"

OR

"Do you happen to know what floor their appartment is on?"

"Do you happen to know with whom Anna left for London?"
"Do you happen to know who Anna left for London with?"
These are both OK.
"Do you happen to know on which floor their apartment is?"
"Do you happen to know which floor their apartment is on?"
These are both OK too.

[ostap77]

"Do you happen to know with whom Anna left for London?"
"Do you happen to know who Anna left for London with?"
These are both OK.
"Do you happen to know on which floor their apartment is?"
"Do you happen to know which floor their apartment is on?"
These are both OK too.

Are there any more formal or less formal?

[bhaisahab]

Are there any more formal or less formal?

You are more likely to hear the second one of each.

[Raymott]

Are there any more formal or less formal?

You'll find that 'whom' is still used after prepositions even by people who never use it elsewhere.

"Who did you give it to?" is more common than:
"To whom did you give it", which is more common than both:
"To who did you give it?" and "Whom did you give it to?"
(In my experience)

[Barb_D]

You'll find that 'whom' is still used after prepositions even by people who never use it elsewhere.

"Who did you give it to?" is more common than:
"To whom did you give it", which is more common than both:
"To who did you give it?" and "Whom did you give it to?"
(In my experience)

In my experience, too.
I think "to who" would be quite uncommon.

[ostap77]

In my experience, too.
I think "to who" would be quite uncommon.

"You wouldn't happen to use "whom" in the middle of a sentence, would you?"

[Barb_D]

"You wouldn't happen to use "whom" in the middle of a sentence, would you?"

Immediately after "to"? You bet I would!

[ostap77]

Immediately after "to"? You bet I would!

How about in speech? Do you say "whom"?

[Barb_D]

Immediately after a preposition? Yes.