Precisely speaking, transliteration is conversion not to another alphabet, but to another script. Polish alphabet is within the Latin script, so you can not transliterate it to Latin - the same as you can not transliterate French é, à, è. You may see also here. But, you can transliterate, for example the Greek, Russian or Japanese alphabet to Latin script.
Perhaps you want to know how that letter sounds?
No, it is standard. In "jabłko" the letter "ł" is mute and "b" is devoiced and pronounced as "p", see http://sjp.pwn.pl/szukaj/wymowa+jab%C5%82ko
For devoicing in Polish, see: https://en.wikipedia.org/wiki/Polish_phonology#Voicing_and_devoicing or better here in Polish https://pl.wikipedia.org/wiki/Ubezd%C5%BAwi%C4%99cznienie
|ProN →||Ja||Ty||On Ona Ono||My||Wy||Oni One|
Jabłko / Jabłka ( Apple/s - Noun Neu ) (dim Jabłuszko ) From Proto-Slavic Ablъko • Diminutive in -kъ of Ablo, from Proto-Balto-Slavic āˀbōl (weak stem āˀbl- Winter's law), from Proto-Indo-European H₂ébōl, H₂ébl̥
Sing → Jabł - ko ko ka kom ko kiem ku ko
Plu → Jabł - ka ka ek kom ka kami kach ka