I have a 1998 VW jetta I'm trying to change the spark plugs. I know the wiring order and the firing order. I just don't know how to tell if the engine is in the right position to be lined up with the firing order.

If your trying to change spark plugs remove one wire from a plug, replace that plug, reinstall the wire onto that plug and move on to the next plug. You don;t need to worry about firing order unless you plan on changing the wires or the cap and rotor. Even if you where to change the wires if you did them one at a time than the new ones would be in the exact same place as the old ones and there is nothing to worry about,

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If you're just changing the plugs, do them one at a time and you will not need to line up anything or worry about the firing order. One wire and one plug at a time. Simple as that.