Uncles funeral

Just read a sentimental poem about life and death?
or just tell her you cannot do it

Stick to what you know.
How long he was married, children, if he had any.
Gardening?
Then a poem.

“Do a reading”- doesn't this mean that a reading has been chosen( could be a poem, or a passage from a book or from from the Bible) and you have been chosen to read it? The correct word for what you are thinking is a eulogy.
Check up what is expected of you. If it is in fact s a eulogy, ask other people who knew your uncle for some anecdotes or ideas.

You need to get together with his closest family and talk about his life experiences, that’s exactly what the vicar would do if he gave the eulogy. You have been asked because you are a confident speaker and not too close that you would get emotional ( that’s hard).
Some eulogies I have heard have been very surprising revealing great endeavor that few knew about.

If you have been asked to do a reading I would find 3 or 4 (not biblical ones if you did not know him well) and then take them to his widow and ask her which she feels would be the most appropriate.

Although you didn't know your uncle very well , doing a reading at his funeral would be a generous thing to do and the last thing you can do for him . I am sure his widow will appreciate it.

If you've been asked to do a reading, the chances are that you will be given the required reading as that is the usual process - ask the person who asked you. If not, then look for an appropriate poem or other passage - there must be plenty to choose from online.

Thank you for your help.
I have asked for help from family but unfortunately he kept to himself. I’m sure I will garner a few gems and be able to put something together for on the day

Thanks all.

I think Septimia is right - the readings may well have been chosen so you will need to know what it is so you can practise it first.
Is it a religious funeral so you could choose a passage from the Bible? If not, there are plenty to choose from online.

Do not Stand at my Grave and Weep
Bilbo's Last Song (At the Grey Havens)
Crossing the Bar

It would be unusual for someone to be asked to do a eulogy if they were not really close to someone. If it is a eulogy, can you think of any happy times you remember with your uncle when you were young, even an amusing anecdote too? Or ask your siblings to help you write it.

Your aunt would need to see and approve first.

A reading is not a eulogy
So you choose something to read - a poem, a passage from literature or something religious (if that is what thy want) but from what you say you have not been asked to speak about your uncle, tell anecdotes or whatever.
You need to discuss this with whoever is arranging the funeral and perhaps the others taking part.
You say “we” have been asked - you and who else?

Look at poems by christina Rossetti and W H Auden. If you Google ‘poems for a funeral’ you will get many suggestions. A reading means just that. You are not expected to talk about the person.