I believe your Elizabeth (nee Yohn) and her husband Frederick Slonaker are buried at the Pottstown Cemetery, East section. I am not doing research on the Yohns, but rather on the cemetery itself.
Section 1,unknown Lot #, according to office records and in Section 5 Row 52 according to the headstone readings we've done.
Space 23.SLONAKER, Frederick(b.10-10-1817 d.3-2-1904) [LDS ? h/o Elizabeth Y. SLONAKER] Space 24. SLONAKER, Elizabeth Y. w/o Frederick (b.4-22-1819d.11-4-1896)
Buried with then in the previous row is Space 23.SLONAKER, Daniel (b.8-18-1793 d.9-5-1870) age 77-0-18 [LDS ? h/o Salome SLONAKER] Space 24.SLONAKER, Salome w/o Daniel SLONAKER (b.?-18-1798 d.7-15-1876) age 85-8-25[LDS ? SLONAKER, Salome (b. 10-18-1790 d.7-15-1876]
We do have a question on a Henry Fronefield Yohn, see new post on Yohn Family forum this date.