You can call getReservesData or getReserveData on the aaveProtocolDataProvider contract, on the pool, or on the UiPoolDataProvider.

These will return a lot of data including:

• currentLiquidityRate: current supply rate. Expressed in ray
• currentVariableBorrowRate: current variable borrow rate. Expressed in ray
• currentStableBorrowRate: current stable borrow rate. Expressed in ray

A ray is a unit with 27 decimals of precision. All the rates (liquidity/borrow/utilisation rates) as well as the cumulative indexes and the aTokens exchange rates are expressed in Ray.

You can call getReserveData on the Pool contract to get rates for a single asset or getReservesData on the UiPoolDataProvider contract to fetch rates for all assets at once. More details here;