The aisle that lemon juice is on in Walmart is usually on or in the baking aisle.
Although in some Walmart stores I've seen the lemon juice in the juice aisle.
It can vary from Walmart to Walmart as they can have things stocked in different aisles in different stores.
In the juice aisle of Walmart the lemon juice is often located near the shelf stable lemonades, lime juice and other bottled fruit juices.
This aisle is where you will find larger multi serve bottles such as Great Value brands or ReaLemon brands of lemon juice.
In the baking aisle of Walmart, the lemon juice is usually stocked on the bottom of the shelves near the pie fillings, baking condiments and extracts.
In the baking aisle you will usually find smaller squeeze bottles or concentrated lemon juice options.
If you can't find the lemon juice in Walmart, you can ask an associate or stocker and they can help you find it or point you in the right direction.