Can you give me examples of personification and onomatopoeia used in "The Red-Headed League"? Thank you.

Onomatopoeia refers to the formation of words that imitate sounds. Good examples include "cuckoo," "sizzle," and "bang." You will often hear people referring to the "clinking" of glasses when they make a toast. The word "clinking" in this sentence refers to a sound; it is another example of onomatopoeia.
There are a number of such instances in "The Red-Headed League," and here are a few of them:

Sherlock Holmes was not very communicative during the long drive and lay back in the cab humming the tunes which he had heard in the afternoon. We rattled through an endless labyrinth of gas-lit streets until we emerged into Farrington Street (p.10).

The word "rattled" refers to the fast movement of the horse-drawn hansom cab through the streets of London.

The light flashed upon the barrel of a revolver, but Holmes’ hunting crop came down on the man’s wrist, and the pistol clinked upon the stone floor (p.10).

We can easily imagine the sound that the pistol makes as it suddenly crashes to the ground. The use of onomatopoeia in such cases serves to make the action seem more vivid.

I beg that you will not touch me with your filthy hands," remarked our prisoner as the handcuffs clattered upon his wrists (p.10).

The sound of clattering handcuffs stands in stark contrast to John Clay's refined, upper-class English accent. It is an appropriate sound, nonetheless, for such a notorious criminal.
Personification is a literary device whereby nonhuman things and objects are endowed with human characteristics. For example, one often hears people say "The traffic slowed to a crawl." Traffic is not actually human—so it cannot literally crawl—but we use personification here to emphasize its slowness. Like onomatopoeia, personification helps paint a more vivid picture of what it is we are trying to say.

It was a poky, little, shabby-genteel place, where four lines of dingy two-storied brick houses looked out into a small railed-in enclosure, where a lawn of weedy grass and a few clumps of faded laurel-bushes made a hard fight against a smoke-laden and uncongenial atmosphere (p.6).

Holmes and Watson have made their way to Jabez Wilson's place of business. It is a rather unprepossessing place as we can gather from this excerpt. The "hard fight" of the weedy grass and the laurel-bushes against the polluted atmosphere helps us visualize the kind of economic condition in which Mr. Wilson finds himself. He does not own a very successful business, and the shabby state of the rows of brick houses and the noxious, hanging air ably reflect this.

It was a quarter-past nine when I started from home and made my way across the Park, and so through Oxford Street to Baker Street. Two hansoms were standing at the door (p.8).

Hansom cabs cannot stand, of course. However, this is a familiar expression and one so much more effective than "two hansoms were outside the door," for example.