You can calculate your exposure intuitively, by calculating your 'fx sensitivity'. Take your total USD assets, let's assume $50k. Convert to EUR at the current rate, let's assume 1 EUR : 1.1 USD, resulting in 45.5k EUR . If the USD strengthens by 1%, this moves to a rate of ~1.09, resulting in 46k EUR value for the same 50k of USD investments. From this you can see that for every 1% the USD strengthens, you gain 500 EUR. For every 1% the USD weakens, you lose 500 EUR.
The simplest way to reduce your exchange rate risk exposure, is to simply eliminate your foreign currency investments. ie: if you do not want to be exposed to fluctuations in the USD, invest in EUR only. This will align your assets with the currency of your future expenses [assuming you intend to continue living in Europe].This is not possible of course, if you would like to maintain investments in US assets.
One relatively simple method available to invest in the US, without gaining an exposure to the USD, is to invest in USD assets only with money borrowed in USD. ie: if you borrow $50k USD, and invest $50k in the US stock market, then your new investments will be in the same currency as your debt. Therefore if the USD strengthens, your assets increase in relative EUR value, and your debt becomes more expensive. These two impacts wash out, leaving you with no net exposure to the value of the USD.
There is a risk to this option - you are investing with a higher 'financial leverage' ratio. Using borrowed money to invest increases your risk; if your investments fall in value, you still need to make the periodic interest payments. Many people view this increased risk as a reason to never invest with borrowed money. You are compensated for that risk, by increased returns [because you have the ability to earn investment income without contributing any additional money of your own]. Whether the risk is worth it to you will depend on many factors - you should search this site and others on the topic to learn more about what those risks mean.