there is no direct way to see all the photos someone likes on Instagram unless they have made their activity public. However, there are a few workarounds you can try:

1. Check Instagram Activity Tab: If you follow the person whose likes you want to see, you can check your Instagram Activity Tab. Tap the heart icon at the bottom of your screen to see your activity feed. You can see which posts your friends are liking, and if the person whose likes you want to see has liked any posts, they will be visible here.
2. Instagram Explore Page: Another way to see what photos someone likes on Instagram is by checking the Explore Page. Instagram’s algorithm shows posts to users based on their interests and activities. If you think you have a similar taste as the person whose likes you want to see, you can check the Explore Page to see what posts are being recommended to you. There’s a good chance that the person whose likes you’re interested in has liked some of these posts too. 
3. Third-Party Apps: There are several third-party apps available on the internet that claim to show you someone’s Instagram activity, including their likes. However, you should be cautious about using such apps as they may be unreliable and violate Instagram’s terms of service. Additionally, using such apps may put your own account at risk of being hacked or banned.

In conclusion, while there is no direct way to see all the photos someone likes on Instagram, you can try the above methods to get an idea of the person’s interests and activities on the platform.

there could be various reasons why someone might want to see what someone else likes on Instagram. Here are some possible reasons:

1. Curiosity: A person might be curious about the kind of content that their friend or acquaintance likes on Instagram. They might want to see if they share any common interests or if there is anything that they could learn from the other person’s likes.
2. Stalking: In some cases, a person might want to see what someone else likes on Instagram as a form of stalking. They might be obsessed with the other person and want to know everything about them, including their social media activity.
3. Marketing: If a person is running a business or trying to promote their brand, they might want to see what their target audience is get comments on Instagram. This could help them tailor their marketing strategy and create content that resonates with their audience.
4. Personalization: Instagram’s algorithm uses the user’s likes to personalize their feed and show them more of what they are interested in. By seeing what someone else likes, a person could get a better understanding of what kind of content Instagram is showing them and why.
5. Relationships: In some cases, a person might want to see what their significant other likes on Instagram to see if there are any red flags or potential issues in the relationship. This could include seeing if they are liking provocative images or engaging with their exes.

It’s important to note that some of these reasons might be considered unethical or inappropriate, and people should always respect others’ privacy and boundaries on social media platforms.