The above comments are in error.
"I met (not meet) a person whose car is yellow." Thus, "I met a person whose car is yellow."
"I know someone whose teeth are white." Or, "I know someone who has white teeth." Or, "His/Her/Their Teeth are white."
"If she likes you, she will give you her attention."
"If someone really likes me, they will show me through their attitude." The proper term is 'attitude' not 'attitudes' as it is singular possessive.
Finally, a higher level writing of the sentence, ""If he really cares about you, he will show you through his attitudes." would be "His attitude will show that he cares about you." Better yet, would be: "You will know that he cares about you by his attitude." Finally, we could write at the collegiate level something like, "His attitude will demonstrate if he cares about you."
Replace (?) with (whose).
I met a person whose care is yellow.
I know somebody whose teeth are yellow.
"Whose" means "belongs to him/her."
"If somebody really likes me, she will show me through her attitudes"
"If somebody really likes me, he will show me through her attitudes"
"If some people really likes me, they will show me through their attitudes"
Notice that I added "me" after "show" because the verb "show" needs an object. "Who did she show? She showed you."
The name of this grammar topic is "possessives." For more on this topic, look up "possessive pronouns."
Hope this helps!