how do i make a block i made check if there is a Ore under it or not?

Always specify the Minecraft version you're using in the thread title.

 

You first need to decide when this check takes place, what triggers it and what counts as an ore block.

 

You can then use

World#getBlockState

to get the

IBlockState

at the specified

BlockPos

.

i added the MC version and i want it to check after a certain amount of seconds/ticks

If the check is fairly infrequent (e.g. once a second), use

World#scheduleUpdate

to schedule an update tick from overrides of

Block#onBlockAdded

and

Block#updateTick

. Perform the check in the override of

Block#updateTick

.

 

If the check is fairly frequent (e.g. once a tick), use a

TileEntity

that implements

ITickable

.

 

In either case, you'll have the block's

World

and

BlockPos

so you can check the block under it.