You can wrap your code in backticks (```) to format it better.
gdp<-PS3$rgdppc %>%. # my object for GDPpc
select(PS3$ccode, gdp) %>% # trying to tell R to select country code + GDPpc
quantile(PS3$ccode, probs = seq(.1, .9, by = .1)) # getting the quantiles
Without having access to your data, we are limited in how much we can help.
FAQ: What's a reproducible example (reprex) and how do I create one?
Your pipeline does not use correct syntax, however. You are piping a vector (first line) into a function that wants a dataframe (second line) and then into another function that needs a vector (third line).
To take a complete guess, I might do something like this:
library(tidyverse)
PS3 %>%
select(ccode, gdp) %>%
filter(gdp >= quantile(gdp, .9, na.rm = T)) %>%
count(ccode) %>%
arrange(desc(ccode))